The wii was unstoppable in its first few years. The console was flying off the shelves. I know most were buying it for wii sports, but nintendo went ham with the first party lineup as well.

Also, during the first year of the Wii was when Nintendo bought Monolithsoft. The studio responsible for Xenosaga, born from the development team of Xenogears, which in turn was made up of developers from Final Fantasy 6 and Chrono Trigger.

Don't forget Actraiser!  Game concept shouldn't have worked, but it was fun as hell.  But I think the first 12 months following the SNES launch were the best 12 months in gaming period.  I really didn't even expect Super Castlevania IV and Final Fantasy IV to be as good as they were.  Final Fantasy IV blew my mind.

NES is weird, because it also had a soft launch in the US.  It was NYC only in 1985, and only in major cities in 1986.  In 1987, it finally went nationwide, which is when I first experienced it.  If I can count 1987 as the launch year, then NES wins, but that is actually 4 years after the original Famicom release in Japan.

Similar things happened throughout Europe. Certain cities got the console way before most places did. And pricing was wildly different; although, that may have been childhood me not understanding exchange rates.

I would definitely say the Wii. That first year launch lineup really helped the system's sales explode for the first few years. Even though most bought it for games like Wii Sports, Mario Galaxy, Twilight Princess, Prime 3, etc. definitely helped! Wii Fit also technically kind of fits into that first year slot as well.

N64 would be a close second. Mario 64 & Mario Kart 64 were huge. N64 was outdoing both Saturn & PS1 in its first year. They weren't able to keep up momentum because games like Banjo-Kazooie and OoT were pushed from 1997 to 1998.

It's the Super NES I think. People aren't properly accounting for not only the 3rd party games it had but also the fact that many of them were exclusive to the SNES.

Street Fighter II on the SNES isn't just "ho hum, a fun game to play!" ... you're talking about the biggest 3rd party game of that time, it would be like the Switch 2 getting GTA VI exclusive in its first year.

Super Mario World
Pilotwings
F-Zero
Sim City
Mario Paint
Legend of Zelda: A Link to the Past
Super Scope 6
Street Fighter II
Castlevania IV
Contra III
Final Fantasy IV
Actraiser
Top Gear
Super Adventure Island
Super R-Type
John Madden Football

Ninja Turtles: Turtles In Time, Super Ghouls N' Ghosts, The Legend of the Mystical Ninja, Joe & Mac, Romance of the Three Kingdoms II, etc. also. 

Super Mario Kart also just misses the cut off here by like a week, it release Sept. 1, 1992 which was just barely a year over the Aug. 23, 1991 SNES release date. That's so close I almost consider it a first year game.