KroniiK's Amazing Training Guide

Level 1-10
Follow the main questline

Level 10-30
Goelms (for OP classess....such as Merc/Mihile/Phantom/Mages)
For non-op classess (sin/dit/etc..) you can try Pigs, and once you hit level 20's visit goelms.

Level 30-40
I did the mushroom kingdom...until level 40, spawns are amazing at the Pepes.

Level 40-120
Azwan PQ (solo or find a party)

Alternative

Level 40-60/65
Scarecrows

Level 75-110
Jesters/Aliens/MP3

Level 110+
LHC/ToT