Well there are not really many choices.
Durburz is inexpensive and has lots of might.
Druzhag's ability to create troops is very useful.
I almost always take Druzhag, as his magic is also quite potent.
If I am playing with lots of Goblins I also take Durburz becuase of his higher courage and his Inspiring Leader ability.
You don't need many heroes. Save on points and take lots of gobbos and monsters.