The worst QB that was 1st pick occurred in 1999 when the Cleveland Browns selected Tim Couch.
As an aside, The Cincy Bengals had pick #3 in 1999 and chose Akili Smith.
BOTH were COLOSSAL mistakes and far worse than the 49ers picking Alex Smith.
Couch and Smith were better than Smith. And neither of them stayed on the team for eight years.
Tim Couch had 11 game winning drives in the four years he played for the Browns between 1999 and 2003, which I believe is a team record. All this for a miserably bad, EXISTENTIALLY BAD expansion team with an abysmal offensive line. His career would probably have been markedly different if he had played for a team with an o-line of even average quality. Just my two cents worth.