Who to rank 4?

Graydrox

I've got 3 rank 4's already. Hyperion, Corvus and Magik. I run full suicides. I also have a 6* Omega Red and Proxima. Who is the next champ to bring to rank?
Notable champs:
Korg
Thing
OML (pending buff)
IMIW
Ghostrider
Void
Red Hulk
Ultron

None of these champs are duped. I'm kind of leaning towards OML and Thing.

GGhost

Thing for variant 2 and defence, Ghost Rider or Red Hulk for quests