Overratedness depends on your current rating. We're not just evaluating the best Jedi, we're asking which Jedi is not as good as they or others claim them to be.
So Luke Skywalker could not be overrated. He's not even an official Jedi, just a late bloomer who got some training in a swamp. The fact that he can even battle Darth Vader is pretty good.
So who IS highly rated? Definitely Yoda. Also Anakin Skywalker, you'll recall that by Episode III his reputation precedes him around the galaxy. Definitely Darth Vader in Episode IV, though it is arguable whether he was still a Jedi at that point. I think Sith and Jedi are different.
We never get a sense of how highly ranked Obi Wan and Qui-Gon Jinn are.
So the two highest-ranked guys are Yoda and Anakin. I gotta be honest, neither is super impressive. Yoda cannot defeat Count Dooku or Emperor Palpatine, both escape. Anakin ends up getting Count Dooku (so maybe he is better than Yoda?) but then Obi Wan kicks his butt. So really Obi Wan is the best. Yoda never has an impressive victory, but then again never comes close to defeat. Anakin good enough to beat Dooku but gets beat pretty badly. Seems like Anakin is more erratic - can be brilliant but also can be beaten.
So I'll say Anakin Skywalker is the most overrated.