The Med is VERY different from a Carribbean sailing. Very intensive and active touring necessary for most ports of call, and so much to see you really have to pick and choose what you're going to devote the short time too.
It's an excellent way to get an "appetizer" of what Europe has to offer, and quite an economical way to see Europe, because land travel, with hotels and restaurants, in Europe can be very expensive.
The Caribbean can be as relaxing as you like. In Europe if you're not on the go in every port you really feel like you're missing something.