With such a wide array of rank names, differing max caps, and sentimentality held by some users, Levels are a great part of the forums, which here in this thread you can discuss favorite levels, levels you don't like, levels you ended up on multiple times, point/level losses, what have you.
These are my favorite levels I've passed through so far:
Level 11, Atomic Punk (my union was made while I was on this level)
Level 12, Rad Racer
Level 16, Magician Lord
Level 18, Flicky
Level 20, Metal Slime (since it wasn't so slow and I loved reaching the 20s)
Level 21, Rescue Ranger
Level 22, Blaster Master
Level 23, Super Bagman
Level 24, I Feel Asleep!!
Level 27, Sheng Long (made my biggest post day, 930, on this level, and became an officer here)
Level 30, Wicked Sick!
Level 31, Ippon! (began hating it, by 50% in I fell in love with the rank name)