Mario Kart 8 is probably objectively the best one, but I’ll still vote for 64. It’s just one of the most fun times I’ve ever had with a video game. It also really meant something to me. You can say that’s nostalgia, which it very well could be, but it’s a powerful thing.
This sums up my feelings, too. MK8 is technically a better game, at least now that Deluxe is out with a proper Battle mode. Better controls, more content. But MK64 holds a very special place in my heart. It came out less than three weeks before my 17th birthday, and my best friend and I spent much of 1997 playing this game. It was incredibly fun, and has aged surprisingly well, plus I adore the soundtrack. And it had the best Rainbow Road IMO. So, while MK8 may be objectively the better game on paper, MK64 is still my favorite in the series.