Who ?

Scorpion- you will regen when placing petrify on opponents from sp2. His awaken ability is super important to finish fights at 100% health in BGs.
Mister Negative- You will regen from degeneration with his awaken ability.

Both Scorpion and Mr Negative are good at sig 20.

ItsClobberinTime

Are those all your options? Personally, I wouldn't use a generic gem on any of them except Herc (unless I had a good amount of them sitting on my stash gathering dust).

MarvelNoob

I gave CGR a generic, haven't regretted it for a second he's so much better with it

coolspiderman17_

CGR is the best option here. Only needs sig 1 and gets so much from just sig 1

ahmynuts

Herc
Hercules done

Another option?
herc again, hes that good

Contact kabam support and tell them you gave herc the gem by accident so they refund it to you and then use it on him again