I agree with others - prot pally, resto shaman, balance druid. Of the 3 I think shaman is easiest for multibox healing. Druid or pally both viable for tanking, but if you tanked with the druid and healed with shaman what would the pally do ?

I have 1 pally, 2 sham, 2 mage group but I use my druid for tanking currently in place of one mage - only because he's fully badge geared for it. I'm dragging my prot pally along to gear him up, after which I'll switch to pally tank and either not use my druid, or use him as balance.