Weak units defend first?

[JJJ]

Seems like the best solution would be, if there's a tie in calculated defense worth, the unit that costs the least defends. Maybe adding something in for Settlers, considering they also cost a population point. if you want to.

[Mithrandir]

That would (generally) be good in cities and fortresses, but out in the open the best defender should always be chosen, because you'd lose both anyway.