- Which faction is stronger? (Necropolis, Tower, or Conflux)

Well, I agree that Conflux is a tough castle=) But not everyone goes for Armageddon, and even if they do, reaching the Grail makes almost any castle invincible... and the Birds, even with their growth, don't provide a significant HP boost=))

Hmm. Indeed. These castles have excellent Grails. Tower - and you can see everything the opponent is doing and catch them at any moment that's inconvenient for them.
Necropolis. A 20% bonus to necromancy and increased skeleton growth. Brrr.
Conflux. All spells and even more birds. A difficult choice.
By the way, I've noticed that the vast majority of posts don't take the Tower into account. And that's a mistake. Perhaps, after losing once to a strong opponent (I had this happen with Fortress, Tower, and Inferno), they would change their opinion and stop underestimating it. The fact that an effective strategy for the Tower isn't widely publicized (a clumsy word), doesn't mean it doesn't exist (or maybe there are several).