My favorite in the main game is The Summit, I really like the music and the double dashes.
My favorite modded level would probably be Paint in Strawberry Jam. There are so many small secrets and details to find, and the art and custom mechanics are great. The music also syncs with the music, which is amazing.
In the base game, Farewell, the music, story, game play, it’s all fantastically put together in the way I love the most.
Modded levels, changes fairly often, but Delusional Canopy probably wins ATM, just a lot of fun if you are able to do the tech in the level.