I've stayed at CSA and did a day visit to CN. I prefer CSA for a couple of reasons:
1) Better beach location. Just turn left and you can hit the many local bars and resorts down the beach. CN sits on Bloody Bay, which is a little more secluded and private. Which is great for those who prefer that...
2) I like the villa-style rooms at CSA more than the hotel-style rooms at CN. We stayed in an Atrium suite and loved the larger veranda and balcony. We also like how the resort was more spreadout which we found allowed for more privacy. Didn't really care for how concentrated the rooms were around the pool at CN.
Both are very nice places, and you probably wouldn't be disappointed in either.