The Rat Caves four(?) floors below West Mountain Path, no question. It's like playing Dynasty Warriors. I do like the areas north of Derby and south of Shipwreck, though. They've got good spawns of a great mix of mobs which're sorely-needed when you're just starting-out in those cities, and you really notice the imbalance in local spawnrates compared to the shoddy experience of trying to level a brand-new character in Durham and to a lesser-extent Dalpok.
I also like the basin at the bottom of the Mt. Shartak Waterfall. That seems to be where the strong jungle mobs (plus alligators) are spawned to congregate. There's no true high-level areas in Shartak of course, but the areas by Mt. Shartak do provide the feeling you're going somewhere more dangerous, which is quite fitting given that Sacred Space is probably one of the first real treks for a character finding their feet.
