ITT: We find out how many people have never owned a dictionary.
what do you mean?
Overate 1. have a higher opinion of (someone or something) than is deserved.
Garchomp? People have a high opinion of it because it is good. Pikachu? Seriously?
Yea, Garchomp is good competitively but most people who have Pikachu/Garchomp on their list don't give a f*** about competitive play. They just think, for whatever reason, that they don't deserve that praise regardless of where that praise is coming from (it can come from things like the anime or competitive play, it doesn't matter to those people) so they're not wrong in their views as all of this is just subjective.
You Trying to Get The Pipe? ~ Earl Joseph Smith III http://theknickswall.com/wp-content/uploads/2013/03/JRSmith-copy-copy.png
I'm gonna go out on a limb and say any Pokemon that has a fairly high usage in OU or Uber despite failing to provide any combat benefit (for instance since Scizor and Escavalier play very differently, they can't be compared for anything other than fire weakness which isn't that big of a deal as 90% of teams will use Politoad.
As for the most overrated Pokemon, it apparently will go "Pika Pika" in game now... 0_o