I don't understand the perverts who voted Life as the worst faction. It has simply magnificent heroes emerging from the Seminary! And their magic is equally impressive. Life magic is the best support for a warrior hero (magic resistance makes it impossible to affect the opponent's hero with curses, but a good blessing can easily give you an edge even against a Barbarian), and Order is the strongest school in the game, it doesn't need any further explanation. Of course, the troops don't bring much joy, but they can't be called completely weak either. And with the support of Tactics, Life, and Order, they become quite decent. The Priest eventually becomes a Paladin and goes to war alone, like a Barbarian (and he does it even better), while the Knight learns Order magic and remains with his army, strengthening it and helping in battle with control.
If I had to choose an outsider, I would name (paradoxically), Might. The troops are only noticeably better than the competition at the beginning, the magic has to be found elsewhere, and the only strong point is the Barbarian hero, unique to this Castle. Indeed, 3 skills instead of two and the starting melee skill are pleasing, but the Nature Ranger, who also has Warfare, is only slightly behind, but the Castle itself offers many more opportunities. Might is a game of blitzkrieg, which can be ruined by an inconvenient group of neutral creatures standing in the wrong place. And the further Might gets from the beginning of the game, the more its lag behind other Castles increases.