Just finished fully exploring Act 8 and opened my 7\* nexus and got this impossible choice:

All three of them are excellent. I love playing all of them although I'm not a master of any of them.
To make it more difficult is that I don't have a strong cosmic 7\*, so if I pull a cosmic R3 gem, Gorr would be my top choice (otherwise, it's Silver Surfer, Red Goblin, The Serpent...).
I still have my class 7* selector to open so I could go for either Domino or Shang-Chi here and then roll the dice on the cosmic crystal.