For drag races the cars I suggest are the Toyota Supra, Camaro Concept and the Ponitac GTO. In all three cars I've done under 7.5 second quarter miles. With the Pontiac I've nearly broken into the 11 seconds for a half mile. All cars have level four parts and are fine going straight, they hardly veer. None are tuned as I don't tune my cars. I haven't tried many other cars except the Drag King car is really bad compared to those ones.
For speed all you need is the new Mitsubishi Evo (same as Ryo's). Fully upgraded I get into the 390km/h area with it un-tuned. My biggest recommendation for speed races are 4WD cars, they are much more stable than any other car. If you can afford it a Lamborghini is probably the best car you can choose.
For grip cars, my Subaru Impreae beats every other car I've used hands down, excluding the Zonda of course. The Lotus Elise is also extremely good for the smaller, trickier tracks. The BMW E46 is a good car, way better than the E92, and you can win it which is a bonus.
Drifting, the AE86 Corolla GTS is a must have, as well as the RX-7 or RX-8, both are relatively similar, my testing hasn't shown substantially whether one is better than the other. The Tokyo Dockyard is probably the hardest course to drift, I strongly recommend getting a muscle car to use on some of the tracks, as well as the Corolla, you might have to try each car on the tracks if you want to get the best possible score.
In my experience with the game, unless you can be bothered tuning, muscle cars are useless in comparison with the other cars (exception being Tokyo Dockyard drifts). The Zonda is worth the money when grip racing. Same with the Lamborghini at speed racing.
I haven't tested all the cars I want to try yet either, will soon.
Some cars are on my PS2 game, other cars are on my PS3 game as well.
Added by: Miko4 Dec 8th 2009, ID#2218