I don't have any preferred class, they're all fun and good to play. Also like the fact that changing character is a a change of path, of rhythm and that you got to adapt your playstyle.
Now, of course, there are some character that i will be less likely to play, mainly because they're ugly. Such as rangers (the weapons are ugly), especially Racast (too noisy). Though, Humar are my "favorite ugly characters" =) I can play them even am not fond of their look. Among the Force, I cannot get myself to play Fonewm for a long time because they're soooo smelly and fishy (talking about their hat, glasses, high heel, clothes...)
By order I play them like this
Hunewearl / Hucaseal >> Fomarl / Fonewearl >> Hucast / Fomar >> Humar >> Ramarl / Fonewm / Racaseal / Racast / Ramar