Smalling was a no nonsense defender. Very fast, strong, great in the air and also very sound in his one on one defending. He didn't mind being pulled wide as he knew how to defend in those situations, probably from playing RB a fair bit. He wasn't great on the ball, but nor was he particularly poor - he looked worse than he was due to his gangly style and long legs - a bit like Varane in that respect.
He was a much better defender than Maguire. Equally good in the air, arguably better, much faster, much better one on one, but not as smooth on the ball. However, I don't think he gave the ball away as much either, as Maguire does.
Great that he's doing well in Roma!