Pick liferoot around Darrowmere Lake in WPL. If you stay in the water no mobs will ever aggro to you and the spawn is good enough you can continuously circle the lake and level from 150-225.
There is a rare that spawns sometimes on the south side of the lake but he's really easy to outrun or flat out avoid. Some 19s have said they have killed him before too.
Most of the mobs in WPL can generally be solo'd on a hunter... just pull carefully and make sure you have a clean area to kite. It might mean a strategic pull plan to get to a node, and it is a lot of work for a few points of herbalism, but its fun.