NES: Metroid (might be Super Mario Bros, but the hours I spent going the wrong direction in Metroid probably gives it the lead)
Super NES: Super Metroid (could also be Street Fighter 2 as that was the main 2 player game we used to play, but the number of hours I spent speedrunning Super Metroid should make this yet another victory for Samus)
N64: Ocarina of Time (This one is easy as I never owned an N64 and definitely put way more hours into it than the runner up, Mario 64)
PS1: This one is very tough to tell. I might have to go with FFVII because of its sheer scope, but Tekken 3 definitely got some love as well.
DC: Revolt, hands down. I enjoyed quite a bit of NFL2K and Soul Caliber, but Revolt was easily the most consistent and most played game from that console
PS2: ATV Offroad Fury (probably the first one, but it could have been the sequel as well. I'd never played a game where you could catch so much air. It really rewarded you for learning the tracks and the controls and definitely was my two player go to title that gen. Smuggler's Run would most likely get the runner up spot)
GC: Metroid Prime (The title that brought me back into the Nintendo fold. Bought the system just to play this one game and was pleasantly surprised with the rest of the offerings including Pikmin, Smash Bros Melee, and Resident Evil 4, but my runner-up would have to be Animal Crossing)
Wii: Wii Sports (Runner up is most likely Excite Truck or Animal Crossing City Folk, but the fact of the matter is that the Wii was a great party system and one that any guest would think was magic. The Wii was probably the only era of gaming where being a gamer and having a particular system made you cooler to the average person visiting your house. Although, to be fair, the original NES may have had that same feel. It's tough to guage since I was 9 when it came out)
WiiU: Mario Kart 8 (The WiiU was a great system, poor sales aside. Some of my favorite experiences would be Lego City Undercover, many of the Eshop games like Unepic or Guacamelee and the epic experience that is Xenoblade Chronicles X, but Mario Kart single handedly saved that console from ever collecting dust. From the super fun multiplayer to the engaging and addictive single player, DLC, 200 CC, and the thrill of realizing how to drift, it's no wonder that Mario Kart 8 Deluxe is the best selling game on the Switch as well)
Switch: Rocket League (There is absolutely no contest for this one. The next runner up would be Zelda Breath of the Wild with easily over 300 hours. But that doesn't compare with the insane amount of time I've sunk into car soccer. Easily the best bang for my buck for any game purchased in any generation at just $20. I haven't even bought any add ons and I'm probably not going to.)
Something that I've definitely noticed about my gaming habits is that while I absolutely prefer single player titles that immerse you in a world and have you collecting new abilities and items, the wacky racers and car games always seem to get the most play. Games like Twisted Metal, Rogue Trip, Smuggler's Run, Excite Truck. And, of course,. the winning titles from many of these generations. I'm not really into sports games or realistic racers (I did enjoy many, many hours on Gran Turismo 3), but these zany, unrealistic titles seem to be arguably my favorite genre. It really took all my hours being obsessed with Rocket League for me to look myself in the mirror and come to grips with it. Now the only question is what will dethrone Rocket League. The future looks bleak for all other titles at this point.