What's interesting, is that everyone here has a varying amount of responses.
It really goes to show the diverse, quality titles Nintendo makes (or games that are found on Nintendo consoles)
Personally, I feel that the developers @ Nintendo go all out with everything they do. They really try to make a game as amazing and to the best of their abilities as they can.
Sure, NSMB Wii may have been "lazy" to some people in the industry, but the perfection was how the levels were executed, and how everything worked seamlessly.
I feel this is Nintendo. I cannot simply name one game that is the "Most Superior" in quality; simply because Nintendo always makes quality titles. Hell, I think a "game" like Wii Fit even demonstrates insane quality in certain ways.
But, if I had to pick one...throughout all my favourites (be the Brawl, Twilight Princess, Wind Waker, Super Metroid, Mario 64, Galaxy, Pikmin 2, Metroid Zero Mission, Metroid Prime 1 - 3...)
Above them all, I feel Ocarina of Time truly shows Nintendo at its absolute best when they make a game.
That game is still the highest rated game of all time, and for a reason. To some people it may have not aged good (to me its still a blast to play though) but it really was the pinnacle of its design.
My hat is off to Ocarina.