I like to try and create heroes with interesting spell list potentials that compliement each other. Alchemy is one of my fave lists and i use alot of empire heroes because they tend to get alchemy by 20th leval

My minotaur alchemist is fun because he is pretty tough and can summon good help and help the economy when resting

Undead archmage is handy to try lots of spell lists i ill probably try a undead druid or healer sometime

Barbarian demon slayer is pretty fun just for kill power - i may have to give up my awesome magic items when he gets good enough to get magic

Made a dark elf theif - hoping on invisible fast assasin with fast conversion time and huge radiuswill work

Also made a lizard druid - hopes on getting naga and treant friends

And if u want to zerg the enemy: Fey merchant. you'll build A LOT of units (if u researched the xp upgrades u will be building lot's of lvl10 or so units)

I respond with Knight Merchant.

Knights / Knight Lords with all the upgraded bits are probably best (vs. ground-only) mobile units against enemies who deal physical damage, since Knights have 50% resistance against those. Elemental damage, if not zerging - is not a challenge, either. :]

Versus some strong opponents, I usually spam them from 5-6 stables. 20-24 fully up'd knights are usually enough to get rid of a base.

ED: And don't forget each Knight Lord is +1 to Morale. :]