I wouldn't be opposed to going on Crystal again for a very good per diem rate. I just wouldn't go on the harmony again because it is a very old ship and I like the shiny new ones ;)
I would like to try the Serenity in the med but overall I prefer a smaller ship and I prefer all-inclusive because you never have to sign for anything, thus you don't feel like a 'customer'. There's no awkwardness when the check comes because there never are any checks. I travelled on Crystal with a group of twelve people. Everyone wanted to make sure they were buying rounds of drinks and it was awkward when someone wanted to pay and then someone else did... and so on. The thing I love about smaller ships is that the drinks just appear when ordered and there is interruption in the flow of conversation to decide who is paying or to sign the chit. Just a personal preference.