Either will work.

Pally/Pally gets you both buffs, and the two most useful auras for your situation.
Both can tank, heal or dps.
So if you decide to go battlegrounds, you could be dual healers or double dps.

The DK in DK/Pally cannot go healer.
But can cover the other two roles.
The rotation will work; basically play the tank mostly and manage healer cooldowns/heals.
If you want to have two different classes for variety, that will definitely work.