To me, it “could be” a toss up between the Snes, N64 and GameCube. The Wii has sold the best financially because of the casual audience it garnered.
The best in terms of versatility is probably the Wii U, mainly because of modding. Without modding, you can still play Nes, Snes, N64, Game Boy Advance, Turbo Graphix 16, etc. The eshop is kind of limited in selection, so that is a drawback. But with modding, DVD playback can be re-enabled because it was originally planned, but wasn’t enabled. Mods can fix that. You can install homebrew, run emulators, play backup GameCube games, etc. Once the Wii U eshop goes down, I’m going to mod my system.
The Switch will probably take the crown once the homebrew community gets up to par with the Wii U. It’s nuts to me what the modding community can do with these systems. Their lives aren’t over just because Nintendo says so.
I definitely have a favorite, and that’s the N64. Though I can’t say it’s the best.
The SNES. It had it all. RPGs, sports, shooters, fighters, puzzles, action games. Huge library. It came out at the right time and had some of the best talent making games. Squaresoft, Rare, Konami, Capcom all in their prime. For me that time in gaming still has not been topped.