Favorite Game (per system):
PC - Half Life 2. HM: Overwatch, Fallout 3, Fallout 4, Bioshock.
Atari 2600 - Solaris
NES - Legend of Zelda. HM: Super Mario Bros 3. Joke answer: Mach Rider
Master System -
Gameboy - Super Mario Land 2. HM: Wario Land, Raging Fighter
Genesis - Road Rash. HM: Sonic 2, NBA Jam, Skitchin, NBA Live 96
Game Gear - The number of batteries and the lack of an AC adapter (right now) makes it hard for me to play GG games.
SNES - Super Mario World. HM: Street Fighter 2, Super Mario Kart, Link to the Past
Jaguar - Val d'Isere Skiing & Snowboarding. Out of the games that I own, this was the most enjoyable one. If I ever get a copy of Canon Fodder, Val d'Isere might not stay atop.
Saturn - Sega Rally. HM: Either version of Daytona USA and Nights into Dreams. Joke answer: Sonic R
Playstation - Crash Team Racing. HM: Medal of Honor
N64 - Mario Kart 64. HM: Donkey Kong 64, Super Mario 64, Tony Hawk 1
Gameboy Color - Not many games that are GBC exclusive that I realllly enjoyed enough to play a significant amount.
Dreamcast - Soul Calibur. HM: Hydro Thunder, Tony Hawk 1 and 2.
Neo Geo Pocket Color - SNK vs Capcom: The Match of a Millennium
PS2 - Dynasty Warriors 4. HM: DW5, DW3. I literally only bought the PS2 to play Dynasty Warriors games.
GBA - Super Mario Advance 2: Super Mario World, or Link to the Past. Outside of remakes, Castlevania: Circle of the Moon is good fun, as long as you have a brighter screen.
Xbox - Halo 2. HMs: Return to Castle Wolfenstein: Tides of War, Dynasty Warriors 3, Outrun 2, Dead or Alive Xtreme Beach Volleyball, Max Payne, Midnight Club 3: Dub Edition Remix
Gamecube - Super Smash Bros Melee. HM: LoZ: Windwaker, Soul Calibur 2, Super Mario Sunshine,
Nintendo DS - I didn't like the DS. Not lefty friendly. I guess Super Princess Peach has a chance of being a game I really enjoy, just need to play more.
Xbox 360 - Dead Space 2. HM: Halo 3, Lara Croft Legend, Tomb Raider (2013), Fear 2,
Wii - Super Smash Bros Brawl
PS3 - Most played game was Uncharted. Haven't played PS3 games much since I got my PS3 replaced with a working one. I've mostly played PS1 games on it.
Wii U - Super Mario Maker. HM: Super Smash Bros U.
Switch - Diablo 3 Eternal Collection. Outside of Collections and Smash Bros. Diablo 3 is really the only game I spend a significant amount of time on. It was time very well spent.
OVERALL: Super Mario World or Half Life 2. HMs: Halo 2, Super Smash Bros Melee, Soul Calibur, Mario Kart 64, Dynasty Warriors 3
Easiest systems to choose from (aka, didn't require me sifting through my library to choose): PC, SNES, Gamecube, Dreamcast, N64, Xbox.
Systems where I spent most of my gaming time outside of PC: Xbox, Xbox 360, Gamecube
For "day 31", I'm going to go through the entire calendar and reanswer all of the questions (except for this one) without looking at my previous answers and see if I can come up with better/different answers.