Loved these two great games. When I got my Wii, these were the first I downloaded instantly. Now to this day, I have managed to complete Mario 64 twice (first time took about 6 years (long story), second time took a week) whilst I still have never ever completed the original game. Best I got is up to Bowser on the final level. That's why I chose to back the original, because it still challenges me to this day and i don't get frustrated with it. It's a game I can pick up at any time and have so much fun and enjoyable.
Yes no doubt Mario 64 is a great for the N64, but it loses its appeal over time, especially after Galaxy came out which took all the best qualities of SM64 and made it even better! Super Mario Bros is a classic, now it's not number 3 or World, but this was the one that caused all them and saved Mario's iconic status forever. As it still challenges me and I enjoy it. I have to back the original.
Vote Super Mario Bros.