there are a few reasons why a lot of people dont' like yoshi
I for one, think he's decent, but i never use him
Once you get to the much better level of playing, these will be more apparent to you:
1. Yoshi has no "third jump" for example, link can jump twice then use his cyclone thingie to get even higher, yoshi has NOTHIGN like that...
2. Yoshi's aerials are... well... not impressive at all, you can't really hit someone in the air out of stage with yoshi
Although he is powerful