I assume we are talking real life football here and not how they will perform in terms of fantasy?
1. RG3, Newton, Kap
RG3 is the next Aaron Rodgers. He really doesn't share much in common with Cam Newton. They have completely different play styles. Cam is a giant, RG3 is a little guy. RG3 is leagues ahead as a passer and is an Olympic quality athlete in terms of his speed.
Kap may end up winning more championships than either of them though.
2. Cam, Kap, RG3
Cam has the biggest chance to never reach his potential. He is still extremely raw and developing as a passer. The jury is still out on Kaepernick I think so let's put him in the middle. I have zero doubts about RG3.
3. RG3, Cam, Kap
I'm guessing you are just talking about numbers here and not in terms of winning a championship.