You can do it both ways but neither way is easy. You can afford more of a supporting cast for a young QB on his rookie contract but that QB is going to experience some growing pains that you're going to have to live with. Once you give your franchise QB a huge second contract then you better draft and develop well, make sure you have top notch coaching, and make tough free agency decisions. The sample size really isn't big enough to see which way is harder to win a Super Bowl with because of the Pats cheating ways in paying Brady under the table. We should know a lot more in ten years.
The biggest mistakes are giving who you think is a franchise qb that big second (or third) contract. Goff, Wentz, Flacco, and Ryan come to mind. Then you have teams that overpaid for a QB who always comes up small in the clutch (Tannehill, Cousins).