Dual-Boxing Synergy

Hey guys i need some advice. Ive been dual boxing for about 2 weeks. I have my Pally and Mage up to lvl 54. Pally is on one account while the mage is on my original account with multiple other toons. I want to be able to switch between multiple toons with range/melee or range/range. Here's how the two accounts are set up right now.

---Account 1---
MELEE-
-Paladin-lvl 54
RANGE-

---Acccount 2----
MELEE-
-Rogue -lvl 70 epic'd out
-Warrior-lvl 70 greens/blues
RANGE-
-Hunter -lvl 70 greens/blues
-Priest -lvl 60 classic wow gear
-Mage -lvl 54 lvling with the pally
-Warlock-lvl 47 (I'm granting him the lvls from my pally)

So my question is, what one class should transfer to my Account 1 that will give me the best synergy with my other classes?

priest