for me, NiGHTS 100%. SM64 is good but was definitely feeling the growing pains of 3D gameplay, whereas NiGHTS was the cumulation of all of the 2D gaming that came before it while also utilizing the new technology available to it's fullest. as an arcade score-attack style game it also has near infinife replayability, and the soundtrack is one of if not the best of all time. i guess it's kind of apples to oranges, though- farer to compare two arcade style games like NiGHTS and Star Fox 64 or two 3D platformers like Super Mario 64 and Burning Rangers
suprised to see how many commenters here haven't even heard of NiGHTS. a remake of the original game is dirt cheap on Steam and definitely worth taking for a whirl. it is a truly amazing game