We also found it hard to chose between them, then we ordered the couples brochure on here and it has a list comparing each couples resort - how many restaurants, swimmings pools etc, so you can chose the one which has the things important to you.
We chose CSA in the end, and will find out if we made the right choice in March!
I don't think you're going to be disappointed with either one, I've heard amazing things about both. We chose to have our wedding at Couples Negril only for the reason that 3 people who have been to both resorts said that the beach at Couples Negril was amazing and they had the best beach out of the 4 resorts. But CSA has more to do so if you wanna be a complete beach bum (like me ) then you'd probably like Couples Negril better. If you're pretty active then I think you'd like Couples Swept Away better. But I agree with the person above me, look at the website and brochures. The best thing I did was get on tripadvisor.com and read the many different reviews and pics from each resort, that should help too! Good luck!