I guess the worst I ever owned was a S&W Model 24 made in the 1980's. I bought it new, worst trigger ever on an S&W gun. Rear of bbl was cut at an angle, gap was like .011 on left side 0..4 on the right, gun would not shoot a group[. Chambers were about .004 oversized. Sent it back to S&W 3 times, they didn't care. They reblued the cylinder the second time a different color blue. I don't still have it.
The second worst is a Kimber Custom II. It's the only gun I've ever bought new that didn't work. It would go to slide lock on the next to last round about half the time. Kimber sent me a modified slide lock. Said if this didn't correct it the gun would have to go back to Kimber for repair. It didn't repair it. I dimpled the slide stop and now it's OK. I had to file the front sight down because it shoots low. I still shoot it but it'll never be one of my favorites.
I really hate to buy anything that doesn't work brand new. Even the Taurus I had worked most of the time.
A new gun ought to at least function.