I think Warlocks would make the best 2v2 group, mainly because the advantages you have as a dual boxer is dmg output, usually focus fire on a single target, but because most successful 2v2 groups have a healer, you will be at a disadvantage in most areas (not having a healer with a brain of their own able to react as fast) Warlocks on the other hand have excellent survivability as well as wonderful DPS on multiple targets. I think this would work best in a 3v3 group (3 locks or 2 locks and a SP) but it would be interesting to see what other dual boxers do in 2v2. I would be entirely surprised if there were any successful 2v2 dual boxers though, anything higher than a 16-1700 rating may be a pipe dream with any classes other than lock/lock or Lock/Spriest or Mage/Mage.