tim couch wasn't that bad compared to some of the others. he has a career completion percentage of 65% i believe...ryan leaf was terrible, but he had injury issues and of course, off-the-field stuff. here's my top 3, in no order:
heath shuler
akili smith
andre ware
shuler was supposed to redefine the quarterback position because of his impressive athletic ability. instead, a QB they drafted in the 7th round that same year ended up having a much better career. everyone's favorite, gus frerotte.
29 career games, 49.2% for his career, 15/33 TD-INT ratio. and despite being labeled a dual-threat, he only has 198 yards rushing for his career on 67 attempts (3.0 avg).
akili smith had one good season at oregon under jeff tedford (same with kyle boller), and somehow became a top 3 pick of the draft. the bengals actually turned down mike ditka's 10 pick trade offer to get ricky williams, because they were in love with smith apparently.
i'm sure they're regretting that one. he only started 17 games in his career for cincinnati.
andre ware was supposed to be a perfect fit for detroit's run and shoot offense, as he ran the same thing at houston to great success. but it just wasn't meant to be i guess. 4 seasons in the NFL, 14 games, 161 passing attempts (only 11 per game).
i'd say based on pure expectations and the resultant play, shuler and ware have to be the tops on the list.
and to answer this question when asked a year from today, vince young.