Druids for their stealth, Paladins otherwise - either of those two boost with an efficiency fringhtenly better than any other classes can ever do it.

For Horde the progression is pretty easy: (give or take a level or two either side)

RFC 10-16.
WC 16-20.
SFK 20-24
SM(GY) 24-26
SM(LIB) 26-28
SM(ARM) 28-30/1
SM(CATH) 30-40
ZF 40-46 (I just hate Sunken Temple... lol)
BRD 46-54/55
STRATH/SCHOLO 54-58

And then I'd just quest 58-60 in Hellfire Penniensual and there endeth the RAF. When I was doing my recently leveled 5-pally team I pretty much followed that with no boosting, adding a couple of levels to the minimums to ensure the tanks survival.