The easiest duo to level is hunters. Two tanks, simple rotations, very little repair costs while leveling, etc. Warlocks would be #2; they're a little more difficult to macro but the VW pet is actually a bit better tank for killing elite quest mobs. Mages would be #3 because you have to manage aggro/CC.

For novices, pet classes are easily the most forgiving. (And no, I don't consider perma-mage-pets as a real pet class.)