That's a hard one to call.....talent wise you would have to go with Joyner but heart wise it's Cox all day.
I've watched Joyner walk up and down the court when she was on a team the wasn't as good to where as Cox makes everyone around her better. Joyner can play out on the wing to where as Cox can't......but again Cox has a i won't ever quit attitude.
To answer your question I feel that Joyner will have the better college career, but it wouldn't surprise me if I was wrong.