Current 3 Boxer, possibly adding 2 more - Class suggestions?

I have been 3 boxing my level 70 Druid, 70 Shaman, and 70 Warlock and am now thinking of adding 2 more to the group. I cant decide if I should add another Shaman and a Paladin, just 2 more Shamans or some other combination. Although adding another 'lock would be fun as well. Any suggestions on the 2 classes that would best support 5man instancing? I have not gotten into any PvP yet so that's not too important to the equation. Maybe it should be :D

Edit: If you choose other please let me know what your thoughts are. Thanks!