Very basically if you like sea days, take the Eastern, if you like more ports, take the Western.
We're seaday folks, so we picked the Eastern.
Next choice would be ports. We wanted a Caribbenan Cruise, so again, Eastern was the pick. Key West is not what I think of as a Caribbean port.
Having said that, I could pass on St. Thomas. Our
Disney cruise was the first time our kids had been to St. Thomas, so at least now they have been there, but since our excursion wasn't until 1 pm, we could have slept in, if not for the crazy immigration situation now there.
We always get off the ship at all ports. My wife and I had been to St. Thomas 4 times in the past, the last three were before this crazy immigration thing, and other lines, and we always used this as a sleep in day, and booked an afternoon excurison.