It´s time for a good old list of "Top of Something" - in this case Unique Units (= UU) in Civilization 4: Beyond The Sword multiplayer. First of all, while the exact order might be subjective (and more for fun then serve a purpose ), I hope the arguments for why a specific unit is good at achieving something are logical and convincing.
There is some tendency towards early era units, but then again there are more of those in the game.
Remember, evaluating a unit´s strength has always to be connected to the game settings it´s supposed to be used in. So Jaguars don´t shine on Highlands nor do they so in a game where choking one opponent at the cost of your buildup will not win you the game since you are playing 7 other players at the same time.
7. Jaguar
Unique unit for Aztec; Replaces Swordsman
+10% city attack
Starts with Woodsman I
era actually used in: Ancient, some Classical
Jaguars are great for choking the opponent and controlling the area around your land. They have 2 moves on tiles that give them a lot of defense bonus and can be build so soon, that only the threat of them potentially coming makes getting and hooking metal the top priority for the players facing them - sometimes at the cost of hooking food or getting a better position for a second city.
6. Skirmisher
Unique unit for Mali: Replaces Archer
1-2 First Strikes
+50% city defense
+25% hills defense
era actually used in: Ancient
Skirmisher can be build without any ressource while making a choke with warriors and archers against the player building them basically impossible. On the other hand they can slow down or completely choke even more then one player during an ancient start teamer. That is because they have great odds on archers and warriors, especially flat both in offense and defense - so no additional action is required to have the dominating unit in terms of strength on the playing field during the early phase of the game while an opponent requires metal in order to fight them without getting slowed down too much - and even then it´s often a costly endevour freeing your land from skirmishes.
5. War Chariot
Unique unit for Egypt; Replaces Chariot
Immune to First Strikes
Doesn't receive defensive bonuses
Can withdraw from combat (10% chance)
+100% attack vs. Axemen
era actually used in: Ancient, Classical
War chariots have two moves and cost 20 hammers (quick speed) just like normal chariots, but have a strength of 5. That is an increase of base strength of 25%. Only the cataphract and the praetorian can keep up with that and the last one is more expensive then the unit it is based on, the swordsman (26 to 30 hammers). Unlike chariots warchariots can be build for a much longer period of time, adding to mass and the ability of 2 moves a decent strength which can combat even spears in 2 vs 1. Also warchariots come with animal husbandry, a very early researched technology, allowing for a kill or at least certain choking of a player who is left without metal at this point.
4. Panzer
Unique unit for Germany; Replaces Tank
Doesn't receive defensive bonuses
+50% vs. armored units
Starts with Blitz
era actually used in: Modern
Modern is all about fast moving stacks - especially including the ability to move quick around the opponent´s land. The unit for that is the tank, since it is the strongest available 2-mover in this era. You do build other stuff, but the tank is the unit of choice most of the time. The Panzer is a tank that additionaly gets an unreal bonus against tanks. 'nough said.
3. Cataphract
Unique unit for Byzantium; Replaces Knight
Can flank attack catapults and trebuchets
Doesn't receive defensive bonuses
era actually used in: Medieval, Renaissance
Knights dominate late medieval, early Renaissance and the Cataphract gets a bonus of 25% on the base strength of a normal Knight. That leaves it virtually without a counterunit. Both Elephants and Pikeman being the counter units to Knights don´t nearly have as good odds in defense or especially offense (pikeman) as other counter units with their favorite "prey" in other eras - and they both do not have 2 moves nor are the unit you preferably are building in late medieval, early Renaissance. Add to that a strategy that involves building tripple promoted cataphracts that have access to anti melee (= shock) or anti-horse (= formation) promotion and you get a unit that is so unbalanced compared to what else is available at its time like probably no other in the game.
2. Impi
Unique unit for Zulus; Replaces Spearman
+100% vs. Mounted Units
Starts with Mobility
era actually used in: Ancient, Classical, Medieval
Impis are spears with 2 moves. What doesn´t sound too spectacular at first is one of the most feared units in multiplayer civilization. For ancient that means that there is a unit out there, that can arrive in your land before you have planted a second city in order to get metal. It can be build with bronze from bronzeworking, which is almost always the first technology you research, it moves twice (almost) no matter what the terrain is and it gets defense bonus from terrain (forest etc.). Impis can take out or significantly slow down two or sometimes even three players - the presence of Zulu alone makes a difference in the way a team facing them has to plan out their game. After the early game harrassment Impis still can be used in surprise attacks due to their mobility promotion, but also during a bigger attack with sheer mass. That´s true for both ancient and classical, where the Impi is the best possible unique unit in most setups. In medieval they still are able to harass an opponent in many situations and afterwards in big masses are a pretty decent counterunit to Knights since 2 of them kill 1 Knight, even 1 Cataphract most of the time.
1. Fast Worker
Unique unit for India; Replaces Worker
Can improve tiles
move range: 3
era actually used in: all eras
The fast worker is the dominating unit of later eras from Renaissance upwards. In modern and future it is a game defining factor, maybe even the biggest for those eras. Without it many super fast rush strategies wouldn´t be possible. That is due to its ability to save turns early on while chopping forest (move on it AND chop in 1 turn) and due to being able to move on forests/hills AND road them the same turn. Modern and Future start teamer without fast workers would look entirely different. In general in all eras fast workers are the best build up advantage you can get. An imperialistic India cannot be beat in its expansion, the difference to normal workers getting ridiculous in later eras. Also the fast worker shines in all game types multiplayer civilization has to offer, from solo games like duels, CTONS and Ironman games to teamers.
Honorable mentioning: (Aggressive) Praetorians
Unique unit for Rome; Replaces Swordsman
Strength 8 instead of 6.
Praetorians in "normal" status are good, sometimes great. They can be used nicely both in offense and defense. Early send out praetorians can slow down the opponent significantly, too. They require ironworking AND iron though and cost a (for early ancient) pretty painful 30 hammers, while an aggressive axeman with shock promotion has very good odds on them and requires only 23 hammers to be build. Still a great unit, useable throughout the entire game of an ancient or classical start game and even very playable in some medieval start strategies.
With restricted leaders the praetorian is not aggressive (both Roman leader don´t have the aggressive trait) hence has no easy (if any) access to shock promotion when spawning. Now with an aggressive leader the obstacles of setting up a running empire and only then becoming a threat are pretty much the same, but if that happens - there is no counter unit. Aggressive praetorians are the strongest possible unit regarding base strength civ has to offer in an ancient and most parts of a classical start. Even then though sitll not the best unit to have - just the strongest
They are very good in 5v5 ancient teamer games in MP as well and could have made this (MP orientated) list another time beating the Jaguar for example.
Also I wonder by the choice of the Cataphract, and in a related article your praise for the Hippodrome, if some outstanding player(s) in your multiplayer community have distorted your view of Byzantium by often playing this civilization well? The Cataphract comes late, and as I recall doesn't receive immunity from first strikes, unlike the base Knight. Also there are two options for opponents to choose to defend against them, the War Elephant and the Pikeman, both of which have parity against the Cataphract right out of the box.
As far as the Panzer, it comes so late its impact is limited. Isn't the game mostly decided by the time Tanks start roaming around? I prefer units like the War Chariot and the Skirmisher which appear very early and turnwise will be valuable for about half the game. I also like Impis, they are very useful little critters, however you won't be taking any cities with them, nor will you be breaking archers fortified on hills protecting resources like iron or copper. They lack punch and their ability to cut off important resources is sometimes reduced if that resource is on a river--meaning roads aren't necessary.
As for the Jaguar, why that and not the Gallic Swordsman? They are both Swordsman substitutes, but the Jag's intrinsic power is reduced to five which I have found leaves the Aztec without a reliable city-taker until Construction. The GS's guerrilla upgrade is more valuable in the long run than the Woodman bonus, especially being as it is the only melee unit that can become guerrilla 3, which stays with that unit through every upgrade the rest of the game. A Celt can build or promote to a Woodsman 3 unit, whereas no one else can have melee or gunpowder city-takers who survive half the time even on failures. As the game goes on the forests and jungles disappear, but the hills remain, and taking cities on hills is much easier with a few G3 Gallic Swords.
In my view overall the best UU bar none is the Praetorian, and in my games as Rome with Augustus or Julius I have little difficulty building them out of the box with Shock if I wish to. I do it with barracks and a settled Great General which you're soon drowning in if you build the Great Wall. Even without the GW, the Imperialist attribute of both the Roman leaders mean Great Leaders come twice as fast anyway, and putting the first two at your top production cities means quickly into your first war you'll be building Praetorians with two immediate promotions.
The second best in my opinion is the Chinese Cho-Ko-Nu. Crossbowman have no true nemesis unlike most units, which makes them more difficult to defend against and that collateral damage just kills large stacks. It doesn't come that late if you make Machinery a priority, which is a useful tech anyway which requires only Metal Casting as a prerequisite.
The third best in my opinion, and a contender for the best of all on some maps, is the Keshik which I was surprised to see didn't even rate a mention on your list. If you like Impis, I wonder why the much more useful and powerful Keshik didn't make your list. That first strike can be so devastating and they too come fairly early and have a long shelf life. Unlike Impis they can take cities and archers fortified on hills protecting resources and supply lines. If half a dozen Keshiks show up from the depths of a forest or jungle into the soft white underbelly of a civ they might be doomed. Impis would just irritate them.
Forth I would put the Gallic Swordsman, for reasons already detailed. As it doesn't require the resource Iron to be built, you can generally get them online quicker than your opponents can their own Swordsmen. Next I would pick the Dog Soldier, especially due to it not requiring a resource to build, which means you can always get a lot of them out early.
The last two in my view would be the Immortal and the War Chariot. I find the Immortal to be useful long after a chariot would be, not as much for killing axemen but for being the first wave of city attackers after the catapults are done as they are still effective against damaged longbowman and are so cheap. I find War Chariots are also useful well into the medieval period for similar reasons, and can be the deciding factor in early games if Horses are easily obtainable.
The Samurai gets honorable mention because it comes late, and has a relatively small window, but is dominant in that time, and usually useful until riflemen and grenadiers appear on the scene.
Thinking about it, I guess I am more inclined towards UUs with a long shelf-life and which can take cities. Your list contains only three true city-takers, and I've found Jaguars to be distinctly lacking in that regard, really no better than Aztec Axemen. The other two show up awfully late, too much so to be much of a factor as I see it.
It´s tough for me to answer you.
The articles I (we, that is Imhotep, Shizanu and me) post are mostly related to LIVE Multiplayer (mostly 2-3 hours games on quick speed lasting for around a 100 turns started in different eras), but in most cases you can apply almost anything said there to Single Player as well. Sometimes more, sometimes less.
Now when I say Multiplayer I speak about games with lots of human vs. human interaction during all stages of the game, games that are started in all 7 eras (hence for example the Panzer for Modern start - if you reread the article you see that I speak about "modern games" or "renaissance games", those mean games started in that era, for example 3v3 Renaissance on small Inland_Sea).
This article has a clear MP perspective unlike few other I´ve written - but says so in the introduction already .
The actual arguments and ranks are derived from about 4000 competetive games for me in tournaments, day-to-day clan matches and extensive training sessions within a clan. I say that because it would be very tough for me to challenge your arguments since we have a different perspective on what we´re actually relating them to. You possibly not having played in those kinds of MP games, not having played in the MP league while me not having too extensive knowledge of SP strategies makes it hard to find a common basis from which to argument from.
I know this is not good argumenting, but "believe" me when I say that for example the Fast Worker I S the best unit when best means most desired on average in all setups played regularly within the MP community that had hundreths of games each day for years. Obviously you A R E right when you say that Fast Workers are not exactly the best on Marathon - but here there is actually no common ground regarding such a list. You cannot mix an evaluation for quick speed with one for Marathon - just won´t work.
If you are interested I will answer all your arguments regarding why I took that unit over this and why I didn´t take another one you wonder about - those would be answers relating to quick speed (though normal works pretty much the same regarding this), human vs. human games.