all custom heroes if properly built are overpowered... and firebomb is just as good as leap btw only takes some more skillpoints, while summon reinforcements can be allmost as devastating as bombard.
My top 5 heroes:
1) Wizard (fireball, lightning, blink, AoE kill)
2) MotW tank (leadership, spear throw, reinforcements)
3) Dwarf tank (toughness, bombard, leap, reinforcements)
4) Uruk-hai (firebomb, reinforcements, leadership, fear)
5) Elf hero (archer spec, tornado, leadership)
That is for HvM, not HvH, though spear throw is kinda neat for HvH as well. For HvH i'd say elf hero with max cripple, will own all heroes above.
Just my 2 cents
Gaming is fun though don't forget to socialise IRL ^^