1 - 20: starter quests and Blue ribbon pigs.
20 - 30: All kind of Golems
30 - 40: Mushroom Kingdom (If you finish all quests you can grind in helmet and spear pepe's.
40 - 50: Or grind CD's or do all quests from blake (You get a badge) in Kerning City Square
50 - 60 Drakes in Sleepywood or Scarecrows.
60 - 70 Jesters if u have a ranged class or if u output good damage, if not i recommend zeta greys.
70 - 90: Jesters, all way to go. OP EXP on these.
90 - 100: MP3, good exp (Not as much as jesters, jesters are op) and they spawn very very quickly (Unlike jesters)
100 - 120: Romeo and Juliet is the best way (Buy a lot of pots tho, they hit hard) if you have a guild that can leash you, then leave Romeo at 110 and start on LHC.
120 - 200: LHC, This castle is fucking op.