Which installment of the Heroes series had the best campaign storyline for you?

The most interesting storyline is in Heroes of Might and Magic V (I've only played Heroes of Might and Magic III, V, and IV). It's the storyline that makes you want to play through the campaigns. In Heroes of Might and Magic III, for some reason, the campaigns aren't as appealing. Maybe it's just that it doesn't compare to Heroes of Might and Magic V anymore.