Your favorite hero...

Perhaps it's not entirely correct, but for me, a hero's appearance is one of the most important criteria. This is also why I love the campaign heroes so much. Moreover, most of them have the most useful abilities compared to the secondary heroes. By the way, I installed a mod that adds campaign heroes, and now I'm playing and enjoying it. I recommend this mod to you as well. Now, here's a list of my best heroes from different factions (judged by appearance, abilities, and starting conditions):
Haven: Frida, Iris
Inferno: Agrael, Deleb
Necropolis: Markel, Lucretia (I don't like the appearance of other secondary heroes of this faction)
Dungeon: Rilaag (of course!), Synitar
Sylvan: Faidaen, Ossir
Academy: Zehir, Ora
Fortress: Tolgar, Ingvar
Stronghold: Gotai, Tilshek

P.S.: Vlad is also my namesake :)