I voted for GB/C and Vboy.
I may have changed one of those two by NES, but I would require total, 100%, or very close to that, compatibility, and I think it is easier to achieve that on either the gb (gbasize) or the vboy, because of the "oh so many" special chips that plague the nes software (mappers, sound expansions and whatnot), and that would be too hard, or maybe impossible, to achieve, I think, so better to put efforts on other machines that offer a good possibility of avhieving that goal.