What is the fastest way to get a level 100 in Maplestory?

Level 1-10, Maple Island.

Level 10-around 15, Job Quests

Do the class hat quest (Crocell, Andras, Etc.) for quick levels at 18

Level 20-30, Rotting Skeletons.

Level 30-50, CPQ

Level 50-60, Grind in the Ludi Clock Tower.

Level 60-80, Sea of Fog PQ or Pirate PQ

Level 80-90, Rex PQ and Magatia quests

Level 90-100 Rex PQ and Gallos or Captain & Kru.

Hope this helps.

Look up the monsters on global.hidden-street.net if you need to.

~Tai