Beginner - Ford Focus ST '06
Intermediate and Advanced - Citroen C4 WRC which i won at Loeb Rally.
The C4 WRC was way overpowered for both Intermediate and Advanced. I would have used a slower car for intermediate but I didn't have anything slower and I am saving my money for a Formula GT so I didn't want to dump credits on building a rally car for one event. As for Advanced I have no explanation, you end up battling cars that should be faster than you, but the AI just can't put up particularly great times.
As for beating rally races, first off if its an AWD car make sure the diff is set to 50/50. Secondly brake early. If you brake early and you are still screwing up the turns, then brake earlier! Keep trying till you get it right. Watch the onscreen map and be set to brake early, brake smooth slowly increasing pressure, and slower downshifts. Also start turning BEFORE you brake. And never snap off the brakes either, just trail off as you accelerate through the turn.
Give that a try let me know how it works out and what other issues you run into, if any, and we can work from there.