Super Mario 64 DS: It was fantastic playing that game with the inclusion of Luigi, since I thoroughly missed him in the 64 version. Plus it was automatically pretty cool since the original was so addicting.
New Super Mario Bros.: Classic Super Mario Bros. games= awesomeness. 3D graphics= awesomeness. Therefore, classic Super Mario Bros. + 3D graphics= Double Awesomeness. I really enjoyed this game, In fact I was just playing it a little bit ago.
New SMB gets more points for originality (heck, I never thought of redoing old Mario games with good graphics). And, overall, I choose New Super Mario Bros.