Well, I guess this depends on how you view a launch. To me it was always a launch period of roughly 3-4 months. It was not until the Dreamcast that a massive launch day happened, and in my view has not been matched since (not that it saved that system).
These are all through the lens of personal opinion.
To me, the Gamecube was the best Nintendo system launch I remember. I know Smash Brothers was a bit after launch (a month?) but that was all my friend sand I played that holiday season. The system was affordable, had several great games (remember that awesome Star Wars game?!) and was varied (Pikmin and Luigi). The only knock I had was no Mario game which was a tradition.
Next is the SNES. Maybe it is psychology, but $199 with a great game didn't seem like that much and the games blew my child mind. This was the future and remember Mario, Castlvania and Final Fantasy were near launch games.
Middle of the pack go to the NES and the Wii U, the former I don't remember as I was 1 and the latter was an average, but not spectacular launch.
Below average goes to N64. This is largely because Mario 64 did nothing for me and their was a massive drought after launch. I didn't get the appeal at all and was not until Zelda years later that I saw potential in the system.
Worst goes to the Wii for me. The biggest title was Zelda and I bought it on the Gamecube (still prefer that version to this day). Wii Sports was a bit of fun with a group, but I was never crazy about it. The whole system underwhelmed me and I found motion controls to be more frustrating than fun. I just felt disappointed in Nintendo with it.
These views on launches mirror my view on the systems as a whole
Tier 1: SNES, NES and Gamecube
Tier 2: Wii U (could move up or down)
Tier 3: N64 and Wii