My favorites that I've been on are of course the Victory and Triumph. Because they are larger ships. Not to mention newer. Although I also liked the Imagination. Not sure why, just it was a nice ship. All of the ships I've been on were great. But Imagination just stands out a little more from the other 2 "Fantasy-Class" Ships I've been on for some reason. The only ships that I would avoid (And this is just my opinion... I've seen people say they love them the most) are the "Holiday-Class" ships. Holiday, Jubilee and the Celebration. Now I say that, just because they are smaller and older. I personally love the larger newer ships. But that doesn't keep me from going on another "Fantasy-Class" Ship.
Because I will be going on the Sensation in November! And just from pictures I've seen of that ship. It looks awesome, especially now since she was refurbished, just recently. Now there is a bar in the Atrium almost like the larger ships instead of some weird looking "Art" thingy that had standing there.