I tend to work on the synergy the classes will bring to the table... I currently have a pally, 3 shams and a druid but I can't help be feel I would get better PVE mileage by replacing the druid with another paladin... yeah Mark of the Wild is nice but 2x blessings and auras could be nicer.

of course if you had 2x druids to go with her mages, you could tank and healer, have some nice melee DPS with 2 cats or moonfire spam in the odd arena... 5x CC anyone?