Yoshi. Here I go Bigman, Lil B, Bwett, etc.
Yoshi... is underrated SLIGHTLY. Let me repeat that. I honestly think Yoshi can be a bit higher, but he's not gonna make a "Sonic" jump up the list. There are some characters I think will always be a bit higher than Yoshi, like Ness, Lucas, PT, Sonic, and Shiek, among others that are fairly close to him on the tier list. I do think he has the potential to rise over Mario and possibly over someone like Zelda if she dropped on the list. Aside from that though, sadly Yoshi will probably either stay in this spot for awhile or jump/move down a spot (I think Jiggs could go over Yoshi, but it's more of a speculation, considering Yoshi has better tournament representation).
I think the problem a lot of Yoshi's have is that unconsciously they form bad habits that make them a bit predictable with their character. I'll give an example of Bwett. He's a good Yoshi, actually a very good Yoshi, but one day Me and Kosmos sat down, played 2-3 games with him, and pointed out his edge/recovery game right down to the mark. We knew when he would try to save his eggs for recovering, how many he would use from the edge, whether he would try to attack or airdodge the first time around when he got up and then what he would do the second time around as well as where he would try to land. Needless to say, after we pointed that out, Bwett thought about what to do for a bit and then he came back and mixed up his game play with considerably better success than what he had before.
We also pointed out things on stage like when we thought he would run and Usmash us, trying to get the kill. After awhile he changed up the way he played considerably and made it much harder to fight Yoshi safely.
Really that's the biggest flaw I've noticed out of Yoshi, is that his player will probably have some bad tendencies that he didn't really think of or that he thought were best until someone points them out. Aside from his bad OOS game and a bit of trouble he has killing, he has some overall solid defensive game play that I think could be utilized better/safer.