Hard to nail down my favorites, but I'll try to narrow it down.
NES:
Legend of Zelda, Metroid, Contra, Battletoads, and
Crystalis.
SNES: A whole helluva lot of games, as I feel that the SNES has one of the best game libraries ever, but my favorites are,
A Link to the Past, TMNT: Turtles in Time, Donkey Kong Country, Diddy's Kong Quest, Chrono Trigger, Super Mario World (my favorite Mario game),
Mega Man X, and
Super Metroid.
There's actually a ton I'm missing for the SNES, as that was one of the few consoles I felt was absolutely stellar.
N64: Much like the SNES, the N64 I feel also has one of the best game libraries, and my favorites are many. My favorites are
Banjo-Kazooie, Ocarina of Time, Majora's Mask (which still holds the title of my favorite game ever made),
Donkey Kong 64, Conker's Bad Fur Day, Super Mario 64 (which is fantastic),
Perfect Dark, Turok, Goldeneye 007, Super Smash Bros., and
F-Zero X.
Game Cube: My list of games here are kinda limited, as I feel the Game Cube's library isn't as strong as the N64 or SNES. Nevertheless, there's awesome games.
Wind Waker, Twilight Princess, Metroid Prime, Super Smash Bros. Melee, and
Super Mario Sunshine are the best games on the console, in my opinion.
However, the Game Cube gave me what I think is the best designed game pad, and that's the Game Cube Controller. Fite me, scrubs!
Wii: In my opinion, I feel that the Wii has the weakest library, as the console itself I feel is a gimmick. However, there's awesome games too. My favorite on the console is
Super Mario Galaxy (which is fantastic).
Wii U: Again, has a weak library of games, but there's still good ones.
Wind Waker HD might be the best remake,
Splatoon is fun, if slightly unbalanced and flawed, and while I was introduced to
Bayonetta from the Xbox 360 originally, I have to give it to both
Bayonetta games for being exactly what I expect out of a spectacle fighter in the Devil May Cry style.
Switch: It seems Nintendo is turning things around with the Switch, as we now have a much stronger library than the Wii or Wii U.
Super Smash Bros. Ultimate,
Animal Crossing: New Horizons, Breath of the Wild (which is fantastic)
, Super Mario Odyssey (which I think rivals
Super Mario 64 in fun and quality),
Splatoon 2 was an improvement on the first one, but still is kinda unbalanced,
Fire Emblem: Three Houses, ARMS (which is fun), and the wonderful
Astral Chain.
Nintendo has definitely improved with the Switch, as I felt there was a dip with the Wii and Wii U.
Now for handhelds.
Gameboy: This one is easy for me, it's
Pokemon Red & Blue.
Gameboy Color: Easy,
Link's Awakening DX, the definitive version of the game if you ask me.
Gameboy Advance:
Golden Sun, Minish Cap, and
Pokemon Emerald.
DS: Easy, the original trilogy of
Phoenix Wright.
3DS: Love the 3DS, my favorite game is the remake of
Majora's Mask (because it's my favorite game of all time),
Shin Megami Tensei IV, Pokemon X & Y, as well as
Pokemon Omega Ruby and Alpha Sapphire,
Phoenix Wright: Spirit of Justice, and
A Link Between Worlds.
I'd love to have a killer library of games like we had back in the SNES days. That console was near perfect. If we did, it might cause me to leave my PC gaming comfort zone.