What Ethernalshiva listed are common areas, if you can get your parties to go to these areas, the exp will be much better due to less competition:

10-14 or 15: Gusgen Mines vs Bones or Maze of Shakrami vs Maze Makers
15-18 or 19: Korroloka Tunnel vs Worms
19-22 or 23: Sauromange Champange vs Beetles in enclosed area near spine.
24-26 : I forget..i think a few level of Qufim or you can try Battlia downs or Jungles
27-30: Either Yhoator Jungle vs Mandies and gob aggro, or you can alternatively go to Yutunga Jungle near the Sea Serpent's Grotto area and kill Makara(pugil) or Sahagin.
30-33: Best to go to Altepa vs Beetles
34-40 you can do Crawler's Nest, or around 37 do hell bats in Gustav with occasional Goblin.
40-44? Beetles in Western Altepa and Quicksands
45-50 i did CN rear Helm Beetles as well as lower level Citadel bats/beetles.


50-54 Kuftal Tunnel vs Robber Crabs
55-60ish is Boyada Tree vs Robber Crabs and Knight Crawlers, you can also try at the upper 50s Cape Terrigan vs pugils or Kuftal Tunnel lower levels for Raptors. once you hit 59ish you can also try big birds or Raptors(bring WHM for Viruna) in Valley of Sorrows.

60-65: 60-63 is Torama in Lab of Onzozo, or Processionaires in Boyada
64-72: Bibiki Bay vs Gob/bird/dhamel. or alternatively if you have it, Sky is a good place.
66-69: Lizards in Den of Rancor

Afterward its kinda hazy to me...;x