#1 will be the best for diving and snorkeling, and there are some good options off-site. There is none of this near #2 (they will offer diving, but it's not very good). None of either near #3.

#2 is very isolated. The only thing you can do around there is on the resort grounds. The coast there is a bit rugged, and beautiful. All of the beaches are quiet, and you may have it all to yourselves, as was the case for my wife and I. This location is the most difficult to get to, 1+ hour on curvy little roads.

#3 is more centrally-located for various tours around that part of CR. The beach there is okay, but not great. You can drive down to Manuel Antonio for a beautiful beach and bodyboarding or learning to surf.