I don't want Kazs one though.The Audi is a prize car (Licence or stars gained)
I think a GTR GT3 (Kazunori) is a gift car too for some steps in the game.
The Z4 is bad to the bone.. I enjoy it the most.From all the ones you've mentioned, the Nissan is the best out of the box. Check out Praiano's garage over in the tuning section for tunes for all 3. I haven't tried any of the tunes yet, but people have commented that it made the Z4 very good