I'd say this one is the most difficult.ĪD 1257 is a big replica of medieval Europe with huge amount of towns and villages, each territory has its own units, and the mod makers really tried to make it as close to real history as possible, so it's pretty epic (it's a lot about lancer knights with beautiful outfits lol). The PoP mod is a hard one, and it has its own map, history, own factions, units, npcs (aggressive ones, not just thieves or bandits) and it's quite fun (one thing I was annoyed by was constant demands from a village elder to come over and solve some problems). Vanilla version is quite fun, but at some point you decide to get full party of mamluks and just shread everything in pieces, then you start feeling that the game starting lacking something more.
I tried Floris, AD 1257, Prophesy of Pendor and Native Expansion.