Here are the generalities on Eastern & Western, then you decide which fits you better:
Terrain: W - Flat Deserty, palm lined beaches, gorgeous clear water.
E - Hilly, jungly, greener with hidden "cove" beaches, nice water.
Water Sports: W - In abundance. Excellent snorkeling/diving. Parasailing, jet skiing, deep sea fishing.
E - Not as prevailant as west. Nice beaches. Some snorkeling in St. John/Thomas.
Sightseeing: W- average. Mayan ruins in Mexico.
E - gorgeous views at every turn.
Excursions: W - Active
E - Scenic
Party life: W- Fabulous. Key West!, Cozumel, Rowdy fun places to hang out.
E - almost non-existant
Shopping: W - Not great. T-shirts, rum cakes, Mexican Chatzkis & such.
E - A lot!, great deals on jewelery, electronics, perfumes, linens.
Ports: W - Lively, active, hot, fun.
E - Pretty, relaxing, scenic
That's the gist of it. If you are more into the relaxing, shopping & scenery, so east. If you are into activity, watersports, partys, go west. Of course these are in general terms, someone may say they had the best snorkeling at Trunk Bay, etc...blah, blah, blah., sure you may get a great deal on a tanzanite in Grand Cayman, Blah, blah, blah. This just gives you an idea of the feel of the cruise and what to expect for each itinerary.
My choice...Western. We love the sports, activity, staying on an island as long as we can. We like to be on the ship,....we LOVE to experience everything we can in a port.
Mrsfuzzmo