I would probably suggest the druids for you first. It gives you several options for spec, so you can use the same druids for tanking, healing, and 2 forms of DPS. You also get the option of stealth, which if you're farming certain bosses for pet or mount drops means you can stealth past trash. You also get flight form, which gives you a quicker means of travel {in that flight form is instant vs the casttime on mounts} and you get travel for for quick in-combat getaways and swim form. Druids also have decent CC with roots and cyclone.

I wouldn't worry too much about different classes. It's really not that much more work to set up a multi-class/multi-spec team vs all the same. Once you get comfortable with the druids, you can just start with them by swapping their roles around and having one tank and one DPS or running one boomkin and one cat or whatever combination you like. Pretty much once the macros are set up, it's the same faceroll if it's all Elemental Shamans or a hodge-podge of classes specs.