Look up ELO rating, should be good enough.
Viewing post in How to calculate arena points? (RP, BP etc.)
Seems pretty good. I guess this would somewhat cap the maximum elo. Since the further you go up , more insignificant the gains will be.
I may implement this one but I still want to check alternatives.
Btw I found 2 different implementations, one that considers number of total games and the other doesn't care about it. The one doesn't care about the total games played looks better to me , since the first one would make it really harder to gain elo the more you play.