Ranger or Bard because they're both extremely versatile.
Bards can do just about anything if they're played right, and I played one on live for about 5 years. The only problem is that they're not as good on emu because of how mobs get bugged if they get mezzed while running. Bard is the only class that keeps me busy single boxing, otherwise im forced to 6 box

Rangers are also great because they can cc, they can help heal, and push out some mean DPS.
Why do I play a warrior? Well because they're required to actually get anything done in this game unfortunately. Also, I don't like having to bug tanks to do things that they've prob already done a million times with other people who are tankless.