You have several good options. CGR or Red Guardian would be my picks. I personally used the gem on Red Guardian, but I already had CGR up. Can't go wrong with either.
Hyperion is a very good option, but I stopped ranking up most of the champions that are available as 7 stars, after ranking up the 6* Gamora and receiving the 7"* the next day.
Wolverine is only good with apoc horseman ability. Go for cgr as if you do a heavy, then a light ending combo and a normal combo then an sp2 it'll remove half of the opponent's health. He's amazing for questing and bg and one of my all time faves.
Comments
2.Red Guardian
3.Stark Spiderman
Hyperion is a very good option, but I stopped ranking up most of the champions that are available as 7 stars, after ranking up the 6* Gamora and receiving the 7"* the next day.