It's easy to win against not so good players if you're using a phalanx faction and they aren't (new players tend to play as Romans so they're screwed), and I never really got into any sort of competitive multiplayer, I only played on LAN against some friends, so phalanxes were key. Egypt, on top of being an anachronistic stew, was very good - the best bowmen (along with Cretan archers), great pikemen, decent cavalry for a very cheap price. Seleucids and Carthaginians were similarly flexible. Greeks and Macedonians were a bit worse, but they had the best phalanx units - although non-elite hoplites wouldn't be able to break through sarissa-armed pikemen.
Breaking a powerful phalanx with the Romans was beautiful, though.
I played Barbarian Invasion more, and my favourite factions there were the Goths (very well-rounded army) and the Eastern Romans.