A+ challenges open after 25+ rank. With each rank you get new challenge.
As for usage of stick or d-pad, I prefer the letter, for it gives me better control of steering, stick is too loose for me. But I am no super racer, maybe I'm wrong. )))
Qirex speed is faster and Altima is not the track where handling is of top priority. And qirex speed's handling is ok anyway. IMHO, of course. )))