I only have first hand experience with NIH SBIR/STTRs, but I have heard good things from acquaintances with NSF funding. Sounds like NSF has put more resources into startup resources and mentorship, like its i-Corps program. I've also heard that NSF program officers are more open to NSF SBIR PIs pivoting their projects along the way, in order to suss out product-market fit. (Note that my impressions may be some years out of date.)
