I dunno what your other teams are like or if you have any DKS in the mix, but since you are still only level 60 I highly, highly recommend you go with DK + 4 shamans (or DK + mage + 3 shamans). You'll be much better off at 80 than with a pally tank, imo. My team is pally tank/mage/3 shamans, although I've stopped running heroics I cleared almost all of them (oculus didnt do) and now I'm leveling a deathknight, and IMO DKs are much better multiboxer tanks than paladins. Unless they announce a lot of tanking nerfs in 3.1 (not much so far) that will continue to be true as well.

And I don't say this lightly either, my pally is in 4/5 T7.5, full naxx25 epics and has over 4k achieve points, but once my DK hits 80 I probably will retire my paladin. The difference in mitigation and the dps difference between the two is night and day, especially as gear gets better.