I have review all heroes and moved them to group from the most useful to the least useful. I considered to following steps:
1) usefulness at lvl 100 r/r+1 5 stars
2) arena-grand arena-raids-portals-guild championship
3) how easy is to acquire the hero(not talking about ucool special offers)
4) how hard is to counter it in arena
5) how easy is to fit him in a team
6) how fun is to play with it.

Group 1:

Turtle fighter
Manipulator
Rose Fencer
Imperial Executioner
Ninja Assassin
Griffin
Soul hunter
Death Mage

Group 2:

Commander
Corrupted Angel
Chemist
Bear Warrior
Vengeance Spirit
Ember Blade
Crossed Knight
Light Bringer

Group 3:

Hidden Needle
Desert Lycan
Queen of Curse
Silencer
Poisoned One
Demon Assassin
Death Bringer
Cloud Walker

Group 4:

Cleric
Dwarf Warrior
Fallen Dominion
Ghost Knight
Master Mage
Disease Bringer
Depths Voice
Arcane Sapper

Group 5:

Scorpion Queen
Psychopath
Machinist
Ghost Musician
Devastator
Death Knight
Chaplain
Troll Princess

Group 6:

Dungeon Keeper
Admiral
Phoenix
Sword Master
Tusked Storm
Witch
Nymph of Sea
Shadow Shaman

Group 7:

Commando
Enchantress
Lunar Guardian
Mystic
Drunken Master
Lighting Element
Old Curse
Shadow leaf

Group 8:

Ancient Protector
Emberstar
Ice Mage
Psychic Sword
Rifleman
Savage One
war chief
succubus

Group 9:

Vanguard Warrior
wizard doctor
professional killer
iron hoof
nature storm
pilot
ferryman
Ice spirit

Group 10:

forest guardian
storm lord
cat fencer
Warrior Monk
Brute
Sniper
Wind Master
Wandering Spearman

Group 11:

Dope King
Iron Dragon
Lightning Master
Mountain
Shallow Keeper
Deathgore


I'll edit it to tell what each hero excels at.
If you don't like the placement of a hero, let me know and i'll reply with my argument.