I think, in order to judge who might be the biggest bust, you have to take into consideration things like:
- draft slot, so guys selected #1 overall have more "bust" impact than a guy drafted #10
- position, so guys who play QB probably have more "bust" impact than, say, an OL
- hype coming out of the draft, so guys judged as "can't miss" have more "bust" impact than less heralded players (probably related to the first item above)
- how long the guy's career was, so a guy who flames out after 3 years is more of a bust than, say, a guy who lingers around the league, however unproductively, for 7 years
- some important stats, like games started, impact plays (TDs), and such, even if there weren't many
- injuries, and the part they played in reducing impact/shortening his career
I think there was a good thread on this during the offseason discussing the biggest Bills draft bust, which touched on some of these issues.
Given all of that, Curry has to be very high on that list, given his draft hype, lack of impact, and short career. A guy like Mandarich would qualify as well, but you could say that he lingered around the league longer than some (didn't he come back after time away from the league?). I still think Leaf has got to be near the top of the list as well.