I'm using Alex now, but haven't really played enough with it to comment- the AI does seem to have a tendency to attack with larger, scarier stacks now than it did with either RTW or BI (and usually doesn't besiege cities with pathetically small armies, or at least merges a larger army in quickly after it does).
The BI naval "invasions" of 2-3 units, randomly from different factions, will drive you insane. Playing as Romani, I was getting random invasions of this sort from Carthage (makes sense), the KH (no contact with them other than trade rights), and Makedonia (same as KH)... They'd land an "army" of a handful of militia hoplies and akonkistai in Italy, then happily besiege a well garrisoned city of mine, be destroyed, agree to a ceasefire, then "invade" again with 2-3 more units a few turns later. Really, really annoying.
BI did do the naval invasions pretty well when I was at war with Carthage though, landing full stacks and all, although they only seemed interested in landing next to Lilibeo or Capua, nowhere else, and sometimes would land and then never actually move to attack anything.
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