I've sailed Jewel, Radiance and Serenade of the Seas. These are, in my opinion, the most beautiful ships at sea.
They are also my first choice when sailing Royal Caribbean.
The downside may be that they do not offer the "stuff" that Voyager, Freedom and Oasis class ships do. No ice rink, Royal Promenade, Flow Rider...etc. They do have the standard Royal Caribbean specialty restaurants and some decent discos and bars.
To me they are elegant ships with a great use of glass that always gives you the feeling that you are at sea. I'm not a big fan of the larger Royal Caribbean ships because of the "mall" like feel they give me and that most of the time you have no idea you are on a ship.