Suck it and see.

You'll understand the basic style of play of whatever you choose quite early on. You won't have invested too much time so you could always reroll.

Paladin/Shaman/Shaman is flexible. You'll have DPS, two sets of totems, plenty of healing. It's definitely the easy road.
Paladin/Shaman/Mage is very flexible. DPS, totems, healing, crowd control, water/food, portals but will obviously be the most complex to manage.
Paladin/Mage/Mage is less flexible. Your tank will be your only source of healing but mages are a hoot to multi-box. Maybe Priest/Mage/Mage might work better but I can understand the desire to take a Paladin; a high level paladin is a nice addition to anyone's accounts.