Android, not only for gaming but everything else. I love how its so customisable and android can run off any mobile hardware (apart from apple devices). So hardware modifications can lead to a very powerful gaming experience which I don't believe iOS provides. I have also read that proportionally, there are more android developers than iOS developers. So there is a very high rate of development in Android, also considering the fact that every Android software release is significantly different (GB, ICS, Froyo, JB etc..). I have used iOS alot for gaming but I think nothing beats Android. Personal preference.