Second place for me would probably be the Wii's library. Of course GCN being my #1 pick and Wii being #2 could be because I grew up with these systems. All of the Nintendo systems have great games in their libraries though.
I would put Wii above NES, SNES & N64 for several reasons though.
Galaxy 1 & 2 are (excluding Odyssey) my favorite Mario games. Actually, if you exclude GCN, Switch and the handhelds, Galaxy 2 is probably my favorite Nintendo game, and Galaxy 1 is probably second.
I have incredibly fond memories with Brawl, MK Wii and several Mario spin-offs (namely Super Sluggers, MP8 & Sports Mix). Also, the Wii has my favorite console Kirby game, Return to Dream Land.