1. Ridge Racer 6 (and 7). By a thousand miles. The course design in 6 was the strongest ever, there was a ton of single-player content, the sense of speed was phenomenal, the online racing was fantastic, the soundtrack was good, and it still looks great today. (Ridge Racer 7 is virtually the same game, but with some mediocre new courses added, occasional frame drops on said mediocre new courses, no anti-aliasing, more and better music, and a totally different but still very fun single-player campaign. 6 is my favorite but 7 is close behind.)
2. Ridge Racer V. Not enough courses, for sure, but what was there was fantastic. 60fps in a mainline home-version Ridge for the first time was sublime, and it played just as good as it looked.
3. Rage Racer. For its day, nothing felt faster, and the courses were tailor-made to showcase the differences between the available vehicles. This game really made you work for some of those victories, but boy, did it ever feel great to nail those corners!
Honorable mentions: Rave Racer arcade, Ridge Racers 1 & 2 for PSP, Ridge Racer Turbo Mode (60fps) on PS1. And the first two games were fun too, just didn't last very long.
I know that not many people feel this way, but search your soul, you know it to be true: R4 is trash. It just happens to be trash with some of the best graphics on PS1, a fantastic soundtrack, and the same high level of course design as the others. It's also pretty amazing that they were able to add a fun story element. But the gameplay was just not fun to me at all, the weakest in the series by far. If you want more detailed reasoning as to why, I already posted that some time ago:
https://www.resetera.com/threads/rt...l-incredible-today.59721/page-2#post-11085811