MarioKart Wii. I used to play that all the time since I was very little, and I would always get my Dad to play, trying to beat him, and he would always win, until last year. Ha, finally better than you Dad, all the practice was worth it lol
I’ve been playing it for like, 7-8 years, definitely the most played. I used to only play that when I was really little, then I played that and New Super Mario Bros Wii, and then around 8-9 I got my 3ds, and that’s when I started to play more games lol
My friends and I would play for hours every day at Sixth Form and I was hardly off it at home, mastering snaking. My time on DS would easily beat out my time on any other by double digit figures, if not triple.
I want to say Mario Kart DS, I was too obsessed with that game as a kid. It's hard to say specifically since there isn't an activity log on the DS Lite where I put in most of my hours. I got three stars on every cup (back when they didn't make it trivially easy to do), deleted my file and did it a second time because I didn't want it to be over.
Either DS or 8. DS was one of the first games I could play online plus it was just an ultra solid entry. I miss the emblem creator.
On a somewhat related note, recently I tried out that MKWii mod that adds like a billion courses and has unofficial wifi. The tracks varied greatly in quality, but I was surprised at how easy it was to find groups online.