I'm pretty sure it's generally accepted/obvious who's the best with each character.
No one has ever outplaced me in a Brawl tournament as Marth, or actually taken out a set against me using Marth, I could almost claim I've never lost a marth ditto in a tournament either, but DEKAR GOTZ ME.
However, when it comes to some characters, such as Meta Knight (hell I can go reasonably even in MK dittos [but dittos aren't the be all end all] against Chris), Donkey Kong, etc etc, where there are multiple players across different regions, it gets really complicated. The best DK user on the eastern seaboard I would definitely believe to be FTS, but then there's a DK user in SA, how would I, or anyone else be able to discern this?
Unfortunately, as a whole, the Eastern States are a lot 'closer' in just about every single way possible than any of the states would be to SA or WA. And of course, it would be a **** fest. And it would also need to be all 'officially' done up, to follow power ranking rules crap (i.e. 5? or so members from the region are on a board who vote, discuss, etc, it's a lot of work).
Anyway, this discussion would be a lot better off in the Australian Smash Tournaments thread/Character rank list. As this topic directly applies to 'it', the best players of every character are obviously the ones who get top 8 with them. And if there's only ONE person, then it's obvious...