This was my thought.

Basically I dual-boxed my ret pally (leader) and elemental shammy (slave) to 80, and still doing the quests/gathering for $$$. (the ret is my main)

So now of the 3 70 to work with, I would like to get another 2 up to 80. (one of the 2 would be the DK)

I was thinking that have the hunter/druid(boomkin). (this is before I thought of DK)

That would leave me the mage/lock to be the DK partner.

Here is the thing though...mages or locks cant heal the dk...

So....the DK would be the leader....

DK/Resto druid (never stop, mass pulls) (Is this the preferred method ? one be the dpser and one be the healer)

DK/lock (seed of corruption spam boom boom)

DK/Mage (arcane exploady boom boom)

DK/Huntar...meh