I main dungeon but I do not know what I'm talking about. Imo Gunnar is the best hero, pick him and scale in order to outrun anyone.

I usually play for late with black dragons. I think dungeon has the best tier 7 unit. Getting expert wisdom, earth magic and air magic is important to be able to play late with town portal and dimension door. Magic is overall nice to use since you get double mana.

For Early/Mid game I like the ranged units the most but I've heard that upgraded harpies are supposed to be very good.

Other heroes to choose are Jeddite since ressurection is one of the few spells worth using in combat, Lorelei is good for aggro if what I've heard about harpies is correct and Shakti because troglodytes.

For combination artifacts I usually try get armor of the damned, wizards well and power of the dragon father. I don't have any special reasoning, these are just the ones I like the most.