I main Meta Knight, and I submain a sizable group of characters that include Pokemon Trainer, Ike, Bowser, Luigi, DK, Kirby, ZSS, Falco, G&W, and Ness. I've played a little bit of everyone, some I don't play well with, some just aren't as good as my submains. Notice I don't really know how to use characters like Toon Link or Pikachu, but I do realize that they're top tier.
The reason I say Meta Knight is the best is because he's easy to use. But don't get me wrong, he's not really a guaranteed win, but consider how I defined tiers a while back. I said that it had a lot to do with the strength of a character versus the margin of error for that character. Meta Knight's got moves, but yea, so do Toon Link and Pikachu. The thing is, though, that the margin of error is huge. This has two major implications:
1) The price you pay for making mistakes don't result in a stock unless you make far too many mistakes.
2) You're allowed many many mistakes, so even if you're completely unknowledeable as far as the player you're facing or even the character you're facing, you can actually learn the matchup IN THE MATCH if you're smart and know how to play Brawl.
That being said, whenever I see a new matchup with a good player and a new character, I try to get a few games in with them and try to learn the matchup and how the character plays. The only character I have trouble with is Pikachu...and possibly a certain Ike who's just wicked good, but even those matchups aren't terribly hard. You can't make mistakes if you're Bowser, because you might as well just jump off the stage. You can make mistakes with people like Pit, but you'll pay for them much more quickly. If you notice, a lot of the higher tiered characters are still light characters, so making mistakes with them will always be a little problematic at least. But Meta Knight has the advantage of a beastly recovery and multiple jumps. Throw in the fact that his approach is arguably the best in the game, and you....well....have your best character.
Pit has a lot of strong attacks, and Pit's recovery is only really bad if you don't take advantage of gliding. Question for you guys, can Pit attack during his upB?