what are the best cars in class
for grip and speed and for overall
especially in c class and b class and a class and s class
What I do is pick a car class, go to the rivals x-p-r-a-b-c-d-e tracks, and look at a few different types of tracks (tight corners vs sweepers vs ovals, etc.) and scroll the leaderboards. Plus, you can often download a good tune from there (click on their score), try it, and see how close you come to their score.
Not everyone likes the same types of cars, RWD vs AWD, rear engine, etc., and driving styles can vary, but this will give you and idea.
However, the leader boards were wiped a while ago, so it is also easy to get in many, many cars with a stock tune and get into the top 1% to 5% depending on your skill level, so at least you can drive the cars you want to in many cases and still do OK.