RET pally, run around with devine storm spam... it's aoe, decent dmg, use seal of righteousness for extra aoe dmg, and it heals as well which helps with aggro and if your slaves get too close will heal them back up if hit by something.

Frost DK would also work very well.

Both these classes have strong instant aoe abilities, can self heal, wear plate and have ranged attacks for grabbing mobs

Edit: But yea, for low lvl boosting, do not use a tank, use a dps, many times quicker