Mini Cooper S sport
I think 18 is far too young to have 2.0 litre sports car.
My first car was a Nova 1.4 SR, which I absolutely loved, and it was fast enough. I am now 31, and just getting the first 2.0 litre car Ive ever had.
Even with 13 years driving experience, Im still going to take it easy until I get used to it. Im not going to start racing young idiots (in THEIR Novas ) at traffic lights just because I can.
I would advise you to get nothing more than a 1.6 - you have years of driving fun ahead of you, and you will be a much better driver in a few years time.