According to
Thief Training Reference - MapleWiki.
Bandit Leveling AreasExp Areas35~45 Cave Of Evil Eye I (Evil Eye)
43~46 Garden of Green / Red / Yellow (Jr. Cellion / Jr. Lioner / Jr. Grupin)
43~50 Cloud Terrace <5> (Toy Trojan)
43~55 Tree Dungeon, Forest Up North III (Curse Eye)
47~50 Dangerous Valley I (Copper Drake)
50~55 Drake Hunting Gounrd (Drake)
55~70 Drake's Meal Table (Cold Eye / Drake / Wild Kargo)
60~70 Sleepy Dungeon V (Dark Stone Gollem)
60~70 Stairway To The Sky I (Cellion / Lioner / Grupin)
67~70 Hot Sands (Lorang / Clang / Tortie)
Money Areas30~35 Orbis Tower Floors 18~20 (Jr. Sentinel)
43~50 Garden of Green / Red / Yellow (Jr. Cellion / Jr. Lioner / Jr. Grupin)
50~55 Lorang, Lorang, Lorang (Lorang)
50~60 Watch Out for Icy Path I (Jr. Yeti)
50~60 The Path of Time <1> (Platoon Chronos)
60~70 Sleepy Dungeon V (Dark Stone Gollem)
60~70 Cloud Park VI (Luster Pixie)
65~70 Hot Sands (Lorang / Clang / Tortie)
65~70 Garden Of Green II (Grupin)
65~70 Dangerous Valley II (Red Drake)
65~70 Forgotten Path Of Time<1> (Soul Teddy)
All Around Areas30~43 Crow Forest / Crow Forest 2 (Crow)
30~43 Wild Boar Land I / Wild Boar Land II (Wild Boars)
43~50 Forest of Animals (Cloud Fox / Flaming Raccoon)
43~50 The Mountain of Cloud Fox (Cloud Fox)
50~55 Orbis Tower Floor 1 (Jr. Pepe)
50~59 Tree Dungeon, Monkey Forest II (Zombie Lupin)
50~60 Cloud Park IV (Star Pixie / Luster Pixie)
50~70 The Dangerous Cave (Flyeye)
50~70 The Forest Of Gollem / Gollem's Temple IV (Mixed Gollem)
60~70 Forest of Dead Trees I-IV (Coolie Zombie)