Since I’ve been playing mostly on randomly generated maps of maximum size lately, I tend to favor heroes for whom it’s easier to upgrade their Special Ability (SA), and where that ability is useful. Of course, this applies to the case where we know our opponents from the start of the game, which requires some knowledge of certain nuances when creating the map. But considering that on incredibly large maps, a mentor is often generated (and on the last one, I even saw 3), this isn’t a problem for any hero. In my opinion, the most useful SAs are those of Inferno, Necromancers, and Sylvan. The rest are more or less irrelevant, and for example, spending 6 levels to upgrade the Summoning skill for Gnomes to achieve absolute defense doesn’t seem particularly worthwhile. And so on.