My time is 1990+. How can we really include Billy Joe Hobert? Did he even start a game? He just came in at the end of one and was terrible, admitted the he did not prepare, and then was cut. We might as well start talking about Jim Ballard and Craig Nall.
It's hard to pick the worst out of Collins, Van Pelt, Johnson and Losman. All of them actually had good games. Collins had some good games including the Colts comeback in 1997, the late season Jets win at Orchard Park and the Dallas win in 1996. Losman had a decent season in 2006. The much maligned Johnson played well at times until Flutie finally left the picture. Van Pelt never seemed to be that great, yet he was able to outplay both Collins and Johnson to win the starting job and had a knack at winning those 9-6 games in 1997.
If I had to pick one, it would have to be Collins. He lost the starting job twice to Van Pelt and the Bills offense rarely looked like a professional one with him at QB. But of course he was good enough to lead the Redskins to the playoffs, so what do I know.