Game-wise, Ryu has been stronger since SF2:Turbo I think. Originally Ken was the stronger, slower one. Then they switched it for some reason and Ryu was the stronger one and ken the faster one in the games. Ken is typically the better/stronger character because of his mixups, speed, frame priority and less vulnerable moveset.
Canon-wise, Ryu and Ken were seen as even but Ken had the edge up until the Dark Hadou started to effect Ryu. Up til then, the case could be made that Ken was the more naturally gifted fighter being even with Ryu who trains diligently while Ken not nearly as much. Again though, once the Hadou tapped Ryu, his potential was just
