Okay, I'll be the dissenting opinion... *lol*
I love the Eastern, and really really didn't like the Western. Here are my reasons, which are my own -- as others have said, it all depends on what is important to you:
1. I really felt the loss of that 3rd sea day... for me, the ship is the main destination, and sea days are so wonderful for doing some wonderful things onboard, or even just sitting on the veranda or on deck and watching the ocean go by. I spent an inordinate amount of sea day time just being a slug in those wonderful deck 4 loungers.
2. Key West is so not a port to me. Maybe an embarkation point, but not a port of call. It's very odd to me to set sail from Florida, sail all night, wake up the next morning, and... still be in Florida? Get me to the Caribbean, stat!

And if you have small children, there just isn't much to do there. I'd rather be at sea.
3. I loved the shopping in St. Maarten... I got the prettiest dress for me and the cutest outfit for my little boy for Tropical Night, and soooo cheap. And there were so many other things there I wanted to buy. Everything in Cozumel and Grand Cayman was either very expensive and/or very unoriginal to me.
4. My biggest pet peeve of all -- the ship stops in Mexico for one whole day, and a tropical part of Mexico, at that, but because of that they take every tropical-themed party and meal and whatever on the ship and instead make it a Mexican-themed fiesta. BLEH. I am on a tropical cruise, to the Caribbean, I want to hear steelpan music and such. It almost made me cry to step onto the ship to the sound of mariachi music. But again, that's just my own personal expectations and what I like and dislike.
That said, I am happily going on the Eastern again next time!
-gina-