As far as writing goes, I would have to say that one of the originals is the best:
Super Mario Brothers Theme (Original)
Sounds janky as shit, but when you take that same music and perform it for real, it transforms:
Boston Symphony Orchestra - Super Mario Brothers Theme
Ulu - Super Mario Brothers Theme
..now that's some jazzy shit.
Harder you say?
NOT ENOUGH MARIO?!?!? OMG!!!
I had years of nightmares with this as the background music:
The Legend of Zelda - Death Mountain Theme