I'm currently going with 1pally x 4shaman because I find it more interesting to have 2 classes and in my extremely limited experience so far (read RFC instance) its just a little less stressful to keep the mobs in front of the group rather than having them aggro ping-pong around my shammy group. Again, your mileage may vary and I could well get to 70 and go roll myself a 5th shammy. I guess the moral of the story is that you can't go wrong either way, just changes the approach in instances a bit.

Remember that one of the big values of having a pally is that at 70 you can have a gathering character with epic flying mount and Crusader Aura. Very uber for gathering.