I've nearly all advanced classes ( except Mara/Sent)
I use nearly all of them for PvE/Story and such, depending on my mood, but most of the time I'm in PvP anyway
But what I'm really playing in 4.0 PvP right now:
Vanguard Tank:
My main and my favourite class/spec since I started this game two years ago ( was the first char I created)...
Love it in PvP, hate it in PvE ^^
Most of the time I'm running around with my VG
Marksmanship Sniper:
Wanted to give it a try with 4.0, and I somehow like it. It's not the easiest thing to PvP as a sniper, but it's still fun.
Used to play a commando heal, but with 4.0 you can really forget commando heal, sadly...
Tried out my sage as heal, but found it too easy and totally boring, so I stopped playing healers.