Which castle is the most difficult?

Lider1, what makes the AI so dumb?) It seems to play quite well, bringing in a melee army. Can you provide some facts? I don't play the third game very often, and I haven't played it online at all (by the way, can you tell me how? I think it's only online via LAN, or am I wrong?). And by the way, I wanted to ask about Conflux - how often is it used in online games, and is it even allowed in tournaments? As well as Necropolis.