To be the most overrated it HAS to be a VERY POPULAR gun. That means it can't be the Taurus Judge or any of the esoteric Desert Eagle Class Hollywood hype guns. Sure, those can be overrated; they just can't be the MOST overrated. The only ones that can be the MOST overrated are the ones that make astounding ridiculous claims that most people believe. That being the case the choices probably are in the Pistol Category GLOCKs and 1911s since they probably far outnumber anything else including the overrated H&K. In my PERSONAL OPINION, GLOCK has this hands down, since in my not inconsiderable experience, the 1911 is much more likely to fulfill it's claims much more so than the GLOCK can and a looong military history that is hard to discredit. The 1911 is the auto pistol by which all others are compared. That has to count for something. The reason GLOCK cornered the LE market was because it was simple for all those non-gun, non-warrior people that make up the majority of police departments nowadays, to operate. And consequently, we have negligent discharges to levels never before approached in law enforcement history. (this by the way, is less of an indictment on the design than it is of inadequate training). Not to mention, plastic just not holding up the way it is claimed. This does not in any way detract from the claims on this board that many people have made regarding their OWN PERSONAL GLOCK. We are speaking of the total numbers and being involved in training for twenty years, I've seen more parts and frames wear out on GLOCKS than on any other platform. The Beretta 92 could probably be up here as well.
In shotguns, the 870 has this category all to itself, and although I prefer a different make and model, this gun is definately NOT overrated. Everything it claims to do it does, and well.
In revolvers, basically you are limited to Colts and Smiths since they have carried the revolver market for so long. Perhaps the Colt is slightly more overrated (meaning not quite as good as they claim), but they do have a formidable history that is hard to argue with.
Rifles? Someone mentioned Winchester Lever Actions. This may be the only challenge to the GLOCKs as the most overrated. The Winchesters (while I love them) really are and always have been an inferior design to other levers of the time who had a pretty fair share of the market. This is another gun that benefitted from good PR, marketing and television exposure. It really isn't as good as it is claimed.
AR-15 and AK/SKS? Maybe, but I think all of those come closer to fulfilling their hype better than the GLOCK does.
I think GLOCK takes it by a hair over the Winchester 94.