Unfortunately, that isn't how Contrary works. Contrary reverses the effects of your own stat changes, not the stat changes of the target via moves like Swagger. If Contrary Shuckle uses Swagger it will still sharply raise the opponent's Attack.
However, if you can, DEFINITELY have a Contrary Shuckle. This is because Shuckle is able to learn the move Shell Smash, and coupled with its already massive defense, after a few of those it can sit like a tank for pretty much the entire battle.
Sturdy, on the other hand, is practically useless. Shuckle's Defensive stats are massive, so if Sturdy somehow kicks in, you know that you EV trained it wrong.