Levels 1-15: Starting area based on your race (e.g., Bree-land, Ered Luin, or The Shire).
Levels 15-25: Bree-land, Lone-lands.
Levels 25-35: North Downs, Lone-lands, or Evendim (Evendim is a great zone for fast leveling due to quest density).
Levels 35-45: Trollshaws, Evendim, Misty Mountains.
Levels 45-50: Angmar, Forochel, Eregion.
Levels 50-60: Moria (begin questing in Moria after level 50 if you have the expansion).
Levels 60-75: Lothlórien, Mirkwood, Enedwaith.
Levels 75-85: Rohan.
Levels 85-100: Wildermore, Western Rohan, East Gondor.
Levels 100-130: Gondor, Mordor, Vales of Anduin, Minas Morgul.