Hmm. I think my order is something like this:

Dustwallow through 42ish, then Feralas which gets me to 48ish, then Hinterlands which gets me to 51ish, then Felwood which carries me through 56 or so, then WPL or Winterspring.

This is all with RAF. Without the triple xp bonus, You'll want to do all of the above, which should get you through most of the 40s, then you can do Burning Steppes/Blasted lands/Searing Gorge for more in the high 40s.