The obvious answer of QB was excluded by the OP (which so many people apparently have not read). Considering the state of our team, i'd have to go offense. Calvin Johnson or AJ Green would be my choice. Rare talents, would force defenses to game plan around them, and in turn help our QB, running game, and other receivers. If i were limited to defense, i'd probably go Ngata.. There is no way to single block him, would penetrate the middle of the pocket, while leaving guys like Wilkerson, Richardson, and the OLB's single blocked. Would help stop the run, and strike fear into the flat footed pocket QB's like Brady along with the rest of our front. I miss the days of Jenkins blowing up pockets and double teams.. Ngata would bring that back.
Factoring in Age and NON-QB in this question: JJ Watt. We would only need to score 10 points to win a game with how FIERCE our Dline could be with that addition. I have no issues winning games with an epic defense and below-average offense.
Hey, since there are no rules in this game anymore, can I pick superheroes? I'm torn between the Hulk (defensive line) and the Juggernaut (left tackle). Hulk's superhuman rage and strength with get him around the edge easily, but Juggernaut is unstoppable in run-blocking and his feet anchor to the ground when he is pass-blocking. And you also have to worry about Hulk turning back into Bruce Banner during a key play.
Starting to wonder if Sanchez slept with some the the users' significant others... To be this blind...
Juggernaut is a little more versatile too, You could easily put him on the D line with that kind of speed and strength.