CruiserKaren - we have done all three in either Jan/Feb - we are New Englanders looking for a warm weather getaway. The only chilly part of was Ft. Lauderdale at night, our first day at sea - a bit breezy but not enough to keep us out of the pool, Nassau was on the cool side, but not cold enough to stop us from going to the beach.
So much depends upon what you want to do and see.
If you want breathakingly beautiful beaches with great snorkeling, and good island shopping then choose and Eastern route that hits St.Thomas-St. Maarten.
If you are looking for something a bit more adventuresome with things like swimming with the Sting Rays(awesome), climbing the falls(amazing), river rafting/tubing, Mayan Ruins, really nice beaches, and some awesome snorkeling then pick the Western route - Grand Caymen, Jamaica, Cozumel.
If you are looking for a port-intensive cruise that is very diverse that will give you a little bit of everything Caribbean then pick the Southern route.- Aruba, Curacaco.