This is tough because we've had so many terrible picks.
I'm gonna go with Losman though for a couple of reasons.
1) If it wasn't for Losman I don't think we draft Lee Evans 13th overall, and instead trade up ahead of Pittsburgh for Big Ben.
2) Also if we weren't able to trade up for Big Ben, and didn't make the trade for Losman, we would've had our 2006 1st round pick... and guess who we could've used that pick on? Arron Rodgers.
So Losman essentially cost us either Ben Roethlisberger or Arron Rodgers.
It's pretty clear Losman was the worst pick in franchise history.