Graduating training? I think a lot of NFLers may have a decent shot. I would assume guys in the WR and smaller molds may have a better shot though because of endurance, but I could be wrong.
I have friends in role positions in the NFL, UFAs that never made it and what not. And I also have a friend that's a Green Beret, and a friend who washed out of SEAL training (that sounds really elementary. I don't know what SEAL training is called).
It's no contest of which is more difficult. And as many have stated it's an incredible mental challenge. I've heard from friends that the ultimate goal is to get you to be able to think perfectly clear in extreme, extreme fatigue or duress.
But on top of that it's still ridiculously physical. My friend who washed out just physically couldn't continue. It devastated him because he's wanted to be a SEAL since middle school, but his body just failed him. Not just during drills or whatever, but the accumulation of wear and tear over weeks of training.