Depends on what you're doing more of. Xcore is going to be a mid kick stick, more power based shots.
The Ribcore is going to be a low kick. Great for a quicker release.
What are your tendencies of a player? If you like the stick flexing in your hands and you take more slapshots as a defenceman, I'd say go with the Xcore.
If you prefer to feel the flex point below your hand and/or find yourself taking more wrist shots or snappers, go for the Ribcore.