rios was more talented that for sure, coria is very overrated, even more than rios.
Guillermo Coria at his best was magic. Also, mentally tough, believe it or not. For a great example of the latter, see his win over Gonzalez at 2004 Miami.
He wasn't even a contender on anything but clay. That alone suggests only talented to a certain extent. Really great talents with a strong work ethic, and reasonably strong mind, are not contenders on just one surface.
Rios.Who was the better pure talent?
I am always going to be biased towards Coria as he represented the last generation of clay courters with actual all-court skills and who didn't just brainlessly bash high % topspin balls like how the nextgen plays on EVERY SURFACE today. He had awesome touch and decent volleys, wasn't unwilling to come in and also pulled the trigger despite his modest power (especially when playing Nadal as it was impossible to put him away otherwise).
Quarter finalist at the US Open on multiple occasions, including with yips trouble in 2005.