Hello. We have done eastern and western 3 times each. I have cruised in Aug, Nov, Dec, Jan, Feb, & March. We absolutely love the eastern, and love that extra sea day. I think a lot depends on personal preference and what you enjoy doing. One of our favorite ports is Key West, FL (western). Yes, I live in FL, but it is a 7 hour drive to KW from the Orlando area...I much prefer getting there on a ship. The western on the Fantasy won't include Key West, but rather Costa Maya. If you have ever wanted to see Mayan Ruins, Costa Maya is better than Cozumel from that...you are only about 1.5 hours away from the Chochoban Ruins...beautiful! Our roughest weather ever was in Dec 2010 on the western...a huge front passed through Cozumel with lots of rain, and very rough seas on the next day at sea. DH and I didn't mind the rough weather while in Cozumel as DD stayed on the ship and we went to Margaritaville. The sea day, we all spent the day inside our stateroom and just relaxed and watched tv, and took naps...rough seas had DD and I laying flat!
I live in Florida, and yes, hurricane season is June-Nov. The best thing about crusing, is you won't sail near a hurricane if one happens to be out there. They even skirt thunderstorms and rainy weather if they can get around. Your ports might change, but your safety won't be in question.
We loved Tortola when the Magic had a scheduled deviation from St. Maarten a few years back. We also love St. Maarten, and St. Thomas/St. John. We have enjoyed Grand Cayman on the western...we have been to Boatswain's turtle farm a few times.
My vote would be eastern, but only slightly edging out western...to me any day on a ship is better than one on land!