You mean Cole (sword guy) Bela (Bow guy) and Stina? (whip girl)
I think the best two heroes are the governor and Nikolas Taslow. They are only available in the full version of the game, but the governor allows the dragon clan and dustriders to build really strong walls, and Taslow allows the dustriders to build a really, really, really strong tower that shoots electrical bombs at attackers. The governor's special is whirling blade, which allows him to strike multiple enemies around him at once. Taslow's special ability lets him destroy any single machine opponent instantly.