When it comes to an individual song -- well, that changes on a pretty regular basis. As my mood changes, as I hear new songs that fit better, the songs that fit me are going to change.

As far as one band hitting the nail on the head... I'm interpreting that as being the band that turns my personality into something audible, and that would have to be He Is Legend. The vocalist's voice has even changed drastically due to loads of cigarettes and whiskey, which happen to be my two favorite bad habits. It's like they were made for me. Haha.
Interesting, though, that they're not my #1 favorite band. Hmm.