In your opinion, which faction is the strongest in Heroes 5? Let's discuss the advantages and disadvantages of each faction.

Haven is still the best faction – thanks to training. Who else can produce so many high-level units if they have enough gold? Although, if other castles, say, the Dungeon, had the same training hall, it would be even more awesome – turning all assassins into witches!

Witches from assassins? You're ruthless, Shevriel. But no offense, how do you imagine this wonderful transformation? :D

Actually, Haven isn't the best because there's such a thing as balance. Their magic is the weakest (orcs don't count), and their initiative isn't very high (an initiative of 8 for an archer is a nightmare), although the hero's combat stats are quite high. Training is indeed not cheap. An experienced player won't give you the opportunity to train a decent army; the ability is certainly useful, but within reasonable limits. In general, a similar situation will arise if, in a long game, a mage fully equips creatures with mini-artifacts with 30 points of Order knowledge; this will give him a decent advantage in battle.