Crystal Waters is nice in that they will cook all meals for you if you want, and I believe they will do the shopping for you. At Nirvana (where we usually stay), it's one meal a day and you get the food. You can pay for more meal service at Nirvana, but it can be difficult since the same crew has to clean the rooms.
I think the beach and grounds are much nicer at Nirvana, lots of shade trees whereas CW only has palapas for shade.
We tried to get in CW for our trip in Jan, but it's fully booked.