I've been there, than that switching from one car to another when the car sucks on the track or if it doesn't feel right. But I've change my ways.
Since I got my YOKOMO BD, I admit the car sucks at first and almost switch to another car co'z of some tweak issues. But I worked with the car and stick with it. Now I'm quite happy with it, I have driving this car for almost a year now and I'm very competitive with it on both carpet and asphalt track.
All cars have there up's and down's and now a days pretty much all of the cars thats out on the market have the same platform and are almost Identical, you just need to find a car that suite your driving style and stick with.