For me Eota has 4 main classes...and obviously each hero may fill more than one class.
Tank
Hero Killing
Support
AoE
Sieger
P.S. Correct me if I'm wrong!

We'll start with the Elves...
Rune Knight--Tank/AoE/Sieger
Aeromancess--AoE
Soul Binder--Tank/AoE/Sieger
Mystic Swashbuckler--Hero Killing
Divine Wizard--AoE
Blazing Priest--Support/Sieger
Time Cleric--Tank/AoE
Infilitrator--Hero Killing/Support/Sieger
Tactician--Hero Killing/Support/Sieger
Arcane Archer--Support/Sieger/Hero Killing
Creeps
Acid Reaver--Tank/Sieger
Scarab--Tank/Sieger
Eldar Treant--Tank/Hero Killing
Dread Shaman--Support
Ice Spinner--AoE/Sieger
Arcane Mistress--Hero Killing/Support
Master of the Hunt--Hero Killing
Grim Hag--AoE/Hero Killing/Sieger
Colossus--Support/Tank
Aboreal Crusader--AoE
Undead
Nepilium--Hero Killing/AoE
Sorrow Liege--Tank/Support
Incarnation--Support/AoE
High Oracle--Hero Killing/Caster
Forlorn Martyr--Hero Killing
Ascendant--Tank/Sieger
Emberwraith--Tank/AoE
Defiler--AoE
Well thats about it, give suggestions/comments.