SNES/Mega Drive - Sonic 1, 2, and 3D Blast were the games I was always playing, so, probably that. If GBC is applicable, maybe Pokémon Blue and Silver takes it, I don't know.
PS1 - No idea, probably the Crash Bandicoot trilogy.
PS2 - Probably GTA: San Andreas.
X360 - All the Guitar Hero and Rock Band games, these were my whole life for a few years. I kinda miss them, actually.
WiiU/3DS - Smash 4, quite easily. But shoutouts to Pokémon X and Y with their 800 hours.
Switch - Smash Ultimate, quite easily. With no real shoutouts this time.