I'll throw my hat in for Re-Volt or however it's spelt.
There was a post the other day about yet another remake of our fire the steam platform (search for RVGL maybe); I haven't looked into that but back in the day of Voodoo graphics it was so friggin' fun to play, but single player and 8-player LAN.
It's gonna be hard to pick, because despite seeming like a pretty shallow genre, there are some pretty wild differences in gameplay. Arcade, Simcade, and Simulator all rely on different populations. People who enjoy Horizon are probably not lining up to play iRacing, and vice-versa.
In my opinion, I'd say one of the early Gran Turismo games, specifically 2 through 4. It was many people's introduction to racing games and, at the time, was pretty cutting edge. That's now changed with the Sim games, but there are plenty of Sim offerings now and it isn't necessarily anything "groundbreaking" being released anymore.
I'm hesitant to agree with Horizon because I personally don't enjoy it at all, but I understand the appeal of the first one, especially in a time where that concept was fairly new.
NFS:U2 Is also up there, due to the era. That was the epitome of late 90s/early 2000s car culture and had a large impact on the scene at the time, and just was a benchmark for the arcade side of stuff for a long time.
Split/second. You could blow up huge chunks of the track, which than changed the route. You could blow up and airport. And it was made by disney, of all studios. Better action than Burnout imho.
I want to say Kirby Air Ride, but I don't know if the City Trial mode that I love it for should even count as a true racing game, it maybe deserves to be a genre of its own. The actual Air Ride race mode is just okay.
So if that doesn't count, I'll say F-Zero GX instead.
Top Gear 3000, for SNES. Honorable mentions to Mario Kart Wii (because steering the controller to steer the car will never not be fun) and Horizon Chase Turbo (which is pretty much a modern Top Gear game).
Just something about the handling of the cars that feels good to me. A good mix between realism and arcade style.
Then there's the rewind time mechanic that feels good and is tweaked based on difficulty (IIRC you get X amount of rewinds based on difficulty with the highest difficulty having no rewinds)
Mario Kart 8 on the Switch! I love the clown kart the most, especially when I beat the heavier kart users with it multiple times in a row, which would sometimes result in multiple Miis shooting up into space one after the other as soon as the lobby screen appeared, which was them quitting the game. Good times!!
My personal picks aren't conventional best racing game ever picks, but I'm saying a tie between either Cartoon Network Racing (specifically on PS2), Sonic Riders Zero Gravity (so much better than the first one in that series), and Hotwheels Beat That (specifically on PS2). It's probably mostly just a nostalgia thing, but they're all my absolute favorite racing games since they're the racing games I played the most growing up.
Where's the Codemasters love? For me, the GRID and DiRT series both strike the best balance between realism and arcadey fun. Huge shame they were bought out by EA.
Also, don't hate me but Sonic & All-Stars Racing Transformed is kind of a better Mario Kart. Though I haven't played MK8.