1. Shadow, awesome class, I love everything about it, (except for the full balance tree)
2. Sentinel, very interesting playstyle, I enjoy it
3. Scoundrel, pretty fun
4. Sniper, I'm still not too sure about this class, it has some cool stuff, but it's not exactly my stlye
5. Commando, didn't like it at all, havent played it in months
those are the classes I've played to lvl 25 or higher