I have done both, though not on Disney. You are right that they are both fun. I don't prefer one over the other, but maybe this will help you decide. St. Thomas and St. Maarten (eastern) are mountainous, hillly islands. They have great beaches and great shopping. The islands visited on the western itinerary are flatter. Grand Cayman is pretty flat, but is a clean, pretty island and seven mile beach is great! Cozumel is nice for the cultural/historical aspects and is said to have a beautiful park with a good beach ( I haven't been there). The excursion to Tulum is excellent if you are into that kind of thing, also I have heard great things about the jeep tour. I am not too into Key West, although some people love it. I guess I would say that in general the eastern is more a scenic/watersports/beach destination and the western is more a sightseeing/cultural destination - except Grand Cayman which is definately more beach/watersports. Good luck with your decision. Whichever one you choose, you will love it and don't put too much time into it because you never know- there could be bad weather and you could end up somewhere else anyway!!