So far I've 2boxed:
- hunter/priest to level 25
- druid/druid to level 16
- warrior/paladin to level 16
- At level 16 I switched the warrior's paladin to a druid, they just hit 20
It all works pretty well. The leveling game was never hard, 2boxing effectively makes it trivial, and the runes just compound that.
I think the hunter/priest combo was the strongest. The hunter pet is just such a strong tank and the priest healing is amazing. They nerfed both after I moved on from them. I want to see how wild strike works on the druid that's paired with the warrior. Warrior's are so gear dependent that my warrior in shit leveling gear is so much weaker than my hunter's pet. And I know as soon as he hits 25 and I get him a few pieces of gear I'll lose interest.
I'm thinking about making a warlock/mage next.