I've been really impressed by Brett Hundley in the time I've spent around him in Indy. He has great leadership qualities and looks you straight in the eye when he's talking to you. I think he has the best chance of improving his stock if he throws well. The rest of his game is already a big plus; if Hundley demonstrates acuity as a passer, he could move up to the bottom of the first round.
As for the quarterback with the most to lose, frankly, I can't pick one out, because I think everyone is better off throwing on Saturday. Auburn's Nick Marshall has everything to gain and virtually nothing to lose by throwing at the combine. While top quarterbacks like Jameis Winston and Marcus Mariota figure to be first-round picks whether they throw well or not, Marshall will be throwing to help NFL clubs determine whether he's a quarterback at all. But since NFL scouts predominantly view Marshall as a cornerback prospect, he has little or nothing to lose by throwing a few bad balls. If he throws well, on the other hand, his versatility to serve both as a No. 3 quarterback and in an NFL secondary could help his draft stock. I like that all the quarterbacks are throwing; I don't think there's any downside to it. The positives for Marcus Mariota and Jameis Winston are that they're stepping up and going through the drills. I don't think anything either one does Saturday is going to surprise anyone. Each has a good arm and presumably will be comfortable with all the throws they will be asked to make.
The one guy it truly could help is a third-day quarterback, East Carolina's Shane Carden. There are some concerns about his arm strength, but I think he will make a good impression. I think Auburn's Nick Marshall has the most to gain from throwing, as it has become apparent that teams are interested in him as an emergency quarterback who can also wind up helping in other areas. Directing Auburn's run-heavy attack, he obviously hasn't had as much time as others to sharpen up his passing skills, but Marshall might show enough to pique coaches' interest and force them to study him more.
The guy with the most to lose might be Southeastern Louisiana's Bryan Bennett, who has a strong arm but will need to answer some questions about his accuracy. If he's erratic during drills, that could turn some teams off.