the Ambassador class has been my favorite fromt he first time I saw it. It's a nice progression from the Connie, just nice graceful lines. I also love the Conistitution refit, Nebula, and Defiant class ships.
I could never really put my finger on why I don't care for the Soverign, maybe because it looks slightly different in every movie, I don't know. It just doesn't look right for some reason.