Anything can boost the low stuff.
As you get higher, you need more of a tank type.

The advantage of a true tank, is that you can boost beyond the RAF cap.
A half geared 80th, can boost in instances to 68th very easily, where the toons can start Northrend questing.
As far as boosting goes, Feral Druids and Prot Paladins have my vote for "best".
But that is subjective, and an opinion.

If you go with the Pally, you'll want several shields.
There's a crafted level 60 or 61 shield, which is relatively cheap.
4 or 5 of these will last just about any boosting session.