Irrelevant now but....
I had the choice between an S3 and the JCW last year. I choose the JCW and haven't regretted it once. The mini is the best FWD handling car I've driven, I had an Evo before it and I honestly think the mini is just as fun to drive even with less grunt. It really is a complete package straight out of the box, the grip it has cornering is amazing and the brakes are fantastic. The usual mini gripes though, small with no room for luggage. It'll take something pretty special for me to sell it. I've put 20k onto it in a year, any excuse to drive it!
The S3 was nice but it was very expensive for what it was, not much driver involvement and just felt a bit flat to drive.
Now looking at getting a Mk6 GTi for a second car (as the new Focus RS is a bit expensive) so I'll be sure to compare both cars if I buy one.