We were at CN last December. It was beautiful. Ocean and pool water was great. It was not as humid as June, the month we were there before. I can't compare CN to CSA, as we trade off years at CTI, which is beautiful, as well. This year we are going back to CN, for the Anniversary! Can't wait.
The weather is pretty much the same year round, with it being a little cooler and dryer (less humidity and rain) in Dec/Jan than over the summer. There's always the possibility for rain, though, year round, since it IS the tropics.
And which is better? Chocolate or Vanilla? It depends on what you like and what you're in the mood for. Look at the pictures. See which one "calls out" to you and go. Don't look back.
We were at CN for Christmas 08 and it was the best vacation ever. I'm sure there were a few sprinkles but I don't even remember them. Perfectly warm during the day and pleasantly cool (for Jamaica) in the evenings. It's a lot easier to get the guys into the attire required by the resort when they're not sweating to death in the evenings.
We have gone to CSA in January several times. The western side of the island is drier than the Ochi side in January. On all of our trips to CSA, it has rained for brief periods, but never an all-day rain or even all-day cloud cover.
We only did a trading places to CN on this past trip, so I really can't compare. However, if you are looking for a huge sports complex with lap pool, and beachfront rooms that are right on the beach, then CSA is for you. If you are looking for an au naturel beach, an enormous swim up bar/pool, and a treehouse to get a massage, then CN is for you.
Some people say the weather is pretty much the same, I disagree. We have been to CN twice in March, much warner and more humid. We have been to CN 3 times in Dec, this coming Dec will be our 4th in Dec. Everytime the weather was different. Always, not as humid. A bit windier - one yr it was so windy I sat on the beach with a beach towel over me to keep the sand from blowing on me, very dry time of year, sorta missed the afternoon showers which made for beautiful sunsets. Still warm enough to swim. Last year was the BEST. Warm, slight breeze, no humid, evenings were beautiful. One of the other Dec we went it was very warm, said it was unusually warm for that time of year. You are going to the tropics, you never know what the weather is going to be. have a wonderful vacation