How do you know who is going to be a winner and who is going to be a loser?? You really dont but I was asked who I would choose as a QB prospect in another post because I don't really see Luck being more than an Ave QB
But just to speak on it, picking QBs is a crap shoot, I would not just go for the sexy pick because everyone else is all over them, I would not pick a QB under 6'3 simply because I would want someone that can see over the O-Line and get a better view of things, Honestly I would WANT a QB thats 6-5 or better and no less than 220-225, dont need a frail QB thats going to be broken up soon as he gets sacked.(not saying that cant happen anyways)
That being said, one process would be to look over all the college football scene to see what teams are having the best defensive passing years and most sacks. I would look at their schedules and conference and strength of each. If a team is undefeated I would look at what team out of all the teams they played was able to pass the ball the best on them (not forgeting the fact that if teams are down they will pass often) but if a team is able to put up decent passing #'s on the best passing defense in the league or a team that makes alot of sacks it means 2 things to me (throw in some other intangibles here and there also like Ints and fumbles and if they scramble 1st instead of trying to make a pass) 1. they were able to make good, quick decisions and put the ball where it should be and 2. that they can make good decisions under pressure of being sacked and not just pull the ball down and run soon as they feel pressure.
This to me is a good make up of a quality QB, will he be a pro bowl? Never know but he will have proven that he can be against quality defenses and pressure and make plays, will he lead his team to victory, not all the time but thats more of a team on a whole issue and not the QB per say issue.
But alot of things would also be based on the team, scheme and coach,coordinators.