I think it just depends on which one works best for your schedule. I have done both, and enjoyed both of them. When it comes to the weather, its hard to say, but January water temps are colder, while air temps were still nice. I personally dont like it sweltering, so it worked great for us. January is cheaper also, and it was wonderful to get away for a break after the hectic holiday season. It gave us something fun to look forward to after everything went back to normal after everyone went back to school. I think you will enjoy yourself whichever month you choose.