There are a lot of ways to measure a great quarterback, but my favorite is how a QB performs in the clutch. The best QBs in the history of the NFL are known for leading their team to victory in the toughest moments with everything on the line. Here's an example:
Your team is down by four and there's two minutes to go. They're at their own 20 with two TO's remaining. You can have any QB in the history of the NFL taking the snaps. All factors being equal, who would you pick and why?