The worst cameras that I have ever owned or used are the Tower 50 and Tower 51. I have also owned a few of the Ansco/Agfa 35mm SLR folders that have defied all attempts to make them work properly though my problems have involved the film transport mechanisms or light leaks far more frequently than shutter problems.
Although completely anecdotal, the best camera I have ever owned is my Pentax K1000 SE. I bought it at a Reno pawn shop in 1984 or 1985, and it spent the next 20 years of its life bouncing around in the glove compartment, or behind the seat, of several pickup trucks in the dusty outback of Nevada, with not one single CLA. And it never missed a beat or missed a picture. For twenty years if there was a family picture or a hunting picture, it was taken with that camera. Only in the last 4 or 5 years have I begun to semi appreciate it and try to take care of it. The only saving grace of those 20 some years of total abuse is that it stayed inside its leather case unless it was taking pictures. That old case looks like hell but at least the camera body is still in decent shape. But God only knows what the inside looks like. I am almost afraid to send it off for a CLA for fear that Eric will tell me it is not salvageable. I would hate to lose it as it is truly the one camera that I own that I can operate whether I am sober or falling down drunk!