Depends what your requirements are. Having stayed at neither but knowing this area well, Ocean Blue is a smaller, more centrally located resort (should you wish to venture off the resort). Majestic Colonial is only 6 months old and very large and sprawling. Ocean Blue is also relatively new, it opened in 2005 I believe (or late 2004).
Have a great time. Wherever you choose to stay, you will be on a spectacular stretch of beach.