I've been playing almost everyday since launch and all my chars are now lvl 60, except Runekeeper and Warden.
The most fun I think is the burglar with its sneaking skills and cunning attacks. You can also pickpocket bosses for uber gear without killing them.
Loremaster is great also and has some cool pets.
Captain is the buff machine and has human pets to carry his banners which give cool boosts.
I found the Guardian a little boring and the Champion is easy to play but also gets a bit boring after a while.
Hobbit burglar for the win.
