Any of them will do. Personally I used the Peugeot 206 Rally Car. Once you start winning the Medium difficulty ones, you'll win most of them anyway, including the prototype Subaru Impreza, which is particularly good. 👍
i used a mitsi evo 5 to start with. its great for the tarmac rallies when tuned up and when you win a few of these you'll win rally cars anyway so id suggest buying a normal car to save your credits as its a lot cheaper.