choice of tank

My current team of 1 shammy , 1 palli , and 1 mage should hit 80 over the Weekend , so i am already looking forward to starting a new 5 man grp. ( want a 5 man grp asap ) :P
I was origonally gonna do 5 x shammies ( mostly to have them all looking the same :P ) , with my end goal being to try heroics i now realise i will probbly have to switch 1 of them for a tank ^^
currently i already have an 80 DK and also an 80 Palli
Would i be best switching 1 of the shammies for a tank and if so would the dk or palli make a better tank.

both work great as a tank.
Pally would prolly take less dmg, easier to tank with.
DK would increase shamans dmg by 13% (unholy)