I'm sure they'd all be great. A lot depends on which resort appeals to you most. We got married at CSA and it was perfect for us.
The biggest difference I think is the fact that the beach locations for the weddings are not private at CSA and CN. People not from the resort can walk by. This wasn't an issue for us, as Couples staff keep people back, but for some they want total privacy.
The gazebo at CSA is more private as it's in the garden, but it didn't appeal to us. We wanted a beach wedding with the sun and sand and turquoise water (and we got just that at CSA!)
So if you do want a private beach with only resort guests, then pick CSS or CTI.
If you want a gazebo wedding I would pick CSS for it's cliffside gazebo's looking out over the water. However, they probably wouldn't be good if you are inviting lots of guests.
Picking Couples (any one) for your wedding is the right choice. They really take care of you and make your wedding special.