I don't like to give up on SMB, just put the controller down and return at a later time or date.

I do however like to get to the point in levels (before I do take a break) where I know exactly what to do and it just comes down to skills/execution.

May seem crazy, but my favorite levels are the End Boss levels (both worlds, escapes included).

I just love it because it's strictly platforming and wall jumping, the core mechanics that you need to be PRECISE with.

Oh and any level in the Salt Factory Dark World, just because I can listen to the music. 

I took down a place called the Temple of Doom in Pankot Palace, India in 1935.