The game is fairly large.

The camps 10,20,30 are fairly decent in all 3 city zones, 40s though uldah zones are head and shoulders better leaves.

Normal partys (not-leve) are actually best outside uldah... above rank 26. Fairly easy to pull 25-26k/hr steadyon these groups which is about around where you will get in leves when you factor in downtime.

All 3 starting zones are made up into multiple zones which can level you all the way to cap. With Corthas and Mordona being more mid/upper level areas only.