I haven’t done a list yet so here goes (no explanations for placement, characters within a tier are placed in no particular order, I’m only considering how good they are on point):
SSS Tier
Phoenix
S Tier
Wolverine, Viper, Magneto, Zero, Dante
AA Tier
Wesker, Ammy
A Tier
She Hulk, Taskmaster, Akuma, Dormamu, Trish
There is a clear divide after A Tier. The remainder of the characters have a very hard time competing against the upper echelon.
B Tier
Doctor Doom, Spencer, Storm, X-23, Dead Pool, Felicia, Sentinel
C Tier
Thor, Jill, MODOK, Super Skrull, Ryu, Spider Man
D Tier
Iron Man, Chris, Morrigan, Cap, Tron, Hulk, Chun Li, Viewtiful Joe
Fail Tier
Haggar, Hsien Ko, Arthur, Shuma Gorath