This is really tough, and I've been thinking about it since first posted. Like others have said, it may change tomorrow because there is a heck of a lot of good music out there... The melody of each of these is top notch. IMO:
The best engineered song of all time.
The song that really introduced me to heavy guitar rock and roll. There have been others since, but this will always be first.
This version of this song. Tommy always a mind blower. Not his song, but I think he does it better than anybody.
The mashup is awesome and just works so well.
Beautiful song for sure, but what gets me is he wrote it when he was 12 years old. That's just nuts.