I initially tried a DK tank with my first 5 man team and after a few days I dropped in a pally and it makes a HUGE difference. DKs are a lot harder to tank with and take a lot more damage than a pally. For starting off 5 boxing I would use a pally, maybe coming back to the DK when your whole team is better geared and the healer is better able to heal the DK.
Just my 2 cents