Concerning Yoshi:
The fluffy dino has a few things in his way to becoming a usable character. Certainly he is not given as much credit as he deserves, but here's a quick breakdown of his pros and cons, and some reasoning behind them.
Pros
- Fast on the ground (This is very true. His tilts and jab come out almost instantly, and his running speed is faster than Toon Link's.)
- Great aerial game (Each aerial has a specific use, whether it's the best damage-racking aerial in the game, a combo breaker, a chaining/WOP move, a spike, or a KO move.)
- Best aerial speed (Not necessarily how long it takes for moves to come out, but he moves through the air at the fastest speed in the game.)
- Spammable projectile (Slower characters on the ground or air and bigger targets have many problems with the eggs, and it can also be used to rack up damage while edgeguarding.
- SA frames on second jumps (This makes it a lot harder to edgeguard Yoshi, not to mention that lack of DJC is actually a buff considering Brawl's physics.)
Cons
- Crappy shield (It can't be jumped out of, but really, that doesn't bother Yoshi as much as how long it takes to attack out of his shield on the ground. This makes him easily pressured and limits his defense game.)
- Somewhat of a big target (This makes for a poor size/weight ratio, since Yoshi can't tank as well as he could in previous games.)
- Recovery relies heavily on second jump (This isn't that big of a problem unless Yoshi's below the stage... if he's level or higher, then he can recover with egg throw. Also note that Yoshi is extremely sucseptible to footstools. In most situations, however, Yoshi's recovery is almost impossible to edgeguard.)
Matchups
I put these under neither pros nor cons, considering that Yoshi's matchups are commonly considered to be crap, even though he can actually do well against some higher tiered characters. For example, he has a lot less of a disadvantage to Snake than most other "established low tier" characters, and he's a good counter to Olimar. (Jury's out on whether he's good or bad against Marth... both characters will say they win.) However, he falls against MK and G-Dub just as much as most other characters, and projectile spams (aka Falco) can hurt him badly due to his slow roll. Against some projectiles, of course, he can spam right back, and his aerials often go through them, but it's hit or miss against spams for Yoshi. He does, however, beat most low/bottom/lower mid characters pretty easily.
Tournament Standings
Sure, I could go on about how "nobody likes Yoshi" and "he's not popular enough", and while that's true to an extent, he should at least have SOME tournament standings. If he wants to be considered better, he should start placing better.
Conclusion
Yoshi is certainly a character with a number of misconceptions, but he does have enough blatant weaknesses to keep him from advancing too much. It does seem like he's better than characters like Captain Falcon and Jiggz who have placed better than him, but until people see some hard facts, they won't be placing him anywhere higher than low.