If anyone were to choose Luck, we would still have to play GB with an Aaron Rodgers lead offense for the next 6+ years.
The choice is obvious, you take Rodgers, immediately pick up two conference wins against a Rodgers less GB, and your in the playoffs for at least the next 6+ years. The answer to this question is so blatantly obvious it isn't funny.
As much as I like J.J. Watt, choosing him, or any defensive player for that matter, would be ridiculous within the context of how the question was asked. It would make for a better question if the OP would have allowed us to pick two players, one offensive and one defensive.