Bmw for me, rwd 3.0 6cyl so much more fun to drive.
For sure the BMW will be the more entertaining drive...better engine too.
The S3 is dull as dishwater to drive...but very efficient.
Sadly, the RWD would make the BMW a showstopper for me, plus the lack of practicality compared to the S3.
I'd certainly NOT be paying £12k for a Cat D S3!