When I've played against Gilgamesh, he's always managed to conquer a big empire, Mehmed-style. Saladin has consistently been one of the best AI leaders in my games. He always ends up being worshipped by most other AIs, building lots of wonders, being in the top tier techwise, and controlling a huge empire mostly acquired peacefully. If attacked, he usually ends up taking a few cities and vassalising his aggressor (who will inevitably end up becoming a diplomatic pariah if he does not become Saladin's vassal). Also, he always seems to found Judaism, and for the most part does an acceptable job of spreading it. As far as I can tell, he achieves this by virtue of a very balanced game strategy, rather than the all-or-nothing pure war/pure tech approach of some of the other high-performing leaders.