Unless you've already done it, I'd recommend Westfall. Stonetalon has some ~15-20 areas, but is mostly for 22-27.
Checking a resource site is good way to get a quick overview of level appropriate areas:
http://db.vanillagaming.org/?zones=1#0+2+1http://db.vanillagaming.org/?zones#0+2+1When playing a warrior solo, especially before 40, I'd always recommend overleveling an area by at least 2 levels, preferably 4.