Western all the way!!
I do like an extra sea day, but it is outweighed by that early morning immigration. Also, the Eastern seems geared to beaches; while I enjoy that, I prefer the more "active" ports on the Western. I love Key West, which is always so bustling with activity (and I've eaten the best guacamole in the world there at the sunset celebration...the Hemingway polydactyl cats are cool too). Snorkeling with the stingrays in Grand Cayman is something that everyone should do at least once in their lifetime, and I never, ever get tired of Cozumel because there is way too much to do there.
Barb