Which castle is the most difficult?

I came back, read this thread, and...
it's a strange question, to say the least.
It all depends on the map, the template, the layout...
If we're talking in general terms, then Inferno is the most difficult:
it requires a decent amount of resources, but not more than some other factions.
Demon units are complex and require experience to use effectively.
You also need to know how to maximize the potential of many of its units.
And probably Tower, on some maps, due to its resource requirements.

Added 7 minutes later

Lider1, what makes the AI so dumb? It seems to play quite well, bringing in a meat-grinder army.
Can you provide some facts?
I don't play the third game very often, and I've never played it online (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.

Yes, that's true, but a lot depends on how the player plays.
If a player doesn't stay put, then all this meat-grinder army will be defeated by a human player with a smaller army, often even half the size.
The AI is dumb in terms of using spells and in terms of its movements.
If the player starts to play poorly, then of course the computer won't give him a chance, but if the game is played at full intensity, then the computer has no chance