The End of Time (Professional Level 11) had a nice touch of relaxation (though the amount of pressure during some parts was insane).
Architect (Professional Level 4) was fun too. More enjoyable creative challenges, and I liked the small amount of roleplay involved (basically all the Help Triggers).
Ice Cavern (Advanced Level 12) was kinda poopy, but the path I found for it (giving me a time of 11.93 I think) made it fun.
I had a great time with Mountain Climber (Professional Level 3). There wasn't anything special about it, I just enjoyed it.
Alpine Heights (Beginner Level 9)has great scenery, challenge, and the way the texturing was used in some parts was fabulous.
Spidermon (Intermediate Level 6) is an absolute troll. :^)
Vexatious also had fun and creative challenges that I enjoyed.
Korzak (Professional Level 13) was a lot of fun, I enjoyed that one. Great challenges (as well as very creative). This is my #1 favorite level in the game.