I will always have a soft spot in my heart for Super Mario 64. That will always be at the top of any list of games that I have. I think most of the Mario games have been quite memorable (besides Super Mario Sunshine, that water backpack gimmick never did it for me). I don't have a 3DS yet, but am tempted to get the 3DS XL in August, just to play the Super Mario game (and Kart).
Heaven forbid Nintendo ever get out of the hardware business, but I think Mario on the 360 or PS3 could do some wonderful things.