I look at someone like Jagielka, and compare Stones to him.
Jags is an out-and-out defender, that's what he is/was best at.
Stones is a different player altogether. With his skill, yes, I think, as davek has suggested, that his best position is probably as a defensive screener in front of a back four, with the ability to see opposing attacks build up and then be best placed to position himself, and also to be the springboard for his own team attacks once in possession. He has shown some excellent skills on the ball, and the ability to pick out a forward pass accurately.