How bad is it to decline the NSF graduate fellowship? Though NSF results aren't out yet for this year, this question's been wracking my brain since I'm heavily considering taking a gap year before grad school. I also haven't been able to find this particular question asked/answered anywhere online and I feel like there are surely others that might find themselves in this same situation, so I'm asking here. 

Basically, I completed my NSF application in the fall with confidence, and then around a month later found out that my subject GRE scores were abysmal. Coupled with a fairly "low" GPA, I ended up not getting into any grad schools except my least-ranked backup school and a waitlist to another backup. I've talked over with my advisor and we agreed that taking a year off to reapply would be good for me. For one, I can retake the exam and possibly get into a wider range of schools, which means more opportunities to choose from. A second consideration is that part of the reason I didn't do well in school, which I only realized recently, is that I had been ignoring my mental health for years (I didn't believe "mental health" was a real thing, oops) and taking a gap year would help me put a year's worth of space between being thrown into grad classes while I heal. I've also already got plans for the year in place--I would be doing full-time research work for both my advisor and as part of a program I was accepted to. I feel like this is the healthiest, best route for me and is the one I'm most comfortable with. 

However, there's still a chance I could win the NSF (which is exceedingly rare and a crapshoot for anyone, I know, but anyone who doesn't withdraw is technically still in the running!), which means I would have to go to grad school next year to accept the award. They removed the option to defer years ago unless you're active in the military or have a medical issue (I assume this means hospitalization, not going through something like CBT). Because it's such a competitive fellowship, I always had the notion that it would be just plain "stupid" to turn it down (unless, of course, you got some sort of better award). However, because of the reasons I stated in the paragraph above, I'm definitely less comfortable with this path. 

In this scenario, which should take priority? Accepting a competitive fellowship at a backup school I'm unsure about, or taking a year off to reapply and have more options (especially at top choice, selective institutions), albeit without the NSF or possibly any sort of external fellowship? Has anyone gone through either route and regretted it? Also, how does listing a declined award (NOT in the context of winning other awards and having to choose only one) look on a CV? For context, I'm interested in attempting a career as tenured faculty in academia (which is also exceedingly unlikely, I know).
There are no consequences to you if you decline the NSF Graduate Research Fellowship.  You did waste the reviewers' time.

If you get the fellowship and do not get into your first choice PhD program, then I suggest contacting your first choice and asking them if they will reconsider.  Many places are happy to have a PhD student they are paid by NSF to take, when the usual situation is they have to pay to get a PhD student.