Arandor
Arleon's campaign was so well received that in the DLC with Lot's campaign, we undo all the redhead's efforts and give the Necros back everything they lost in the first campaign). In the end, the only thing that matters is the execution of the crowd favorite Silkpul, which triggered the frogs to go to war against Arleon as well. And the redhead's scary friend (the one with the axe) we leave out in Barya's campaign.
Brother Hillar from Lot's first campaign is the best character in the game. And overall, Lot is clearly the developers' favorite faction.
Well, Silkspul (that's what I call him) does start to seem like a decent guy by the end of all the campaigns. And the fact that the humans have two black women — I didn't even realize that at first, because they look alike. There are already too few heroes there, and for some reason they add identical ones on top of that, no idea why they couldn't have made one of them a man or just come up with a different design. The Necros do look like a more pleasant faction, although the humans are fine unit-wise too. The other two are so-so, though the Mechanics had a chance.
And this game showed me that the HoMM devs did well when they decided to dilute the ugly factions with humans, even if just in the form of heroes, like with the Swamp. Because when the whole faction is frogs and lizards, it gets really boring.