Damage, Durability, Quickness, Abilities - main features that characterize a unit. Each stat should add every of this feature to a hero, but in a different way. Strength gives base damage, Finesse - range for the attacks, Intelligence - crit chance, Constitution - amount of action points. It could be changed, you may give a finesse-based unit lower cooldowns.
In terms of durability: strength for vitality, finesse for dodging, intelligence for avoiding disables, constitution for resistances.
Thats the logic. You should first determine what classes you want to have, than determine what each of the attribute may offer to the class and than balance all of this stuff in order to avoid super-imba classes.
