Itīs 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 unitīs strength has always to be connected to the game settings itīs supposed to be used in. So Jaguars donīt 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 itīs 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 opponentīs 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 donīt 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 doesnīt 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. Thatīs 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 wouldnīt 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 donīt 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