I would want to look deeper than what I see on video, and the track stats that some think are so relevant. Yes, the basics of size, strength and speed have to be there, but they are not enough. I want to know more about his psychology/temperament. Is he resilient or easily discouraged? Down 21-0 in the 2nd quarter, is he going to give 30% less focus and effort? Is he tenacious and persistent or always in need of external motivation? Is his preparation for and play in a less than glamorous game (NC State) going to be consistent with his enthusiasm for an FSU game? Can he handle complexity and changes in scheme game-to-game? Is he a follower/conformer who needs approval or can he stand against pressure when things go badly? Above all, I don't want a dim or stupid quarterback. We need someone with the ability to absorb the whole playbook and internalize all of its intricacies so that in every situation he makes the right choice with lightning speed. Accuracy is equally important. A super strong arm is way down the list, as is mobility.
Also I think it's important to keep an eye out for a very few special recruits who have the above qualities at extremely high levels and hopefully spread them throughout the units. They will be your team leaders that hold everyone else up to a standard. They don't have to be the most physically telented compared to the rest of the team, but the force of their personality can elevate those around them.