S3 comes to £6k more than the GTI when speced to the same level as my order.
Its offering more power (which is desirable in this size vehicle why exactly?) but its not offering style or heritage like the GTI is. I doubt 99 out of 100 people would know what an S3 is or be able to recognise it. But you always know a car is a GTI, even when you don't know. Let me explain. Every now and then a Golf catches the corner of my eye, or is in the distance ahead on a motorway and I think "damn, the Golf looks good..." and when I get closer guess what, its a GTI. Its that subtle styling that sets it apart even from far away. Never happened with an S3 or an A3 for that matter.
To be honest if I had that extra £6k I would keep it and grab the GTI. Otherwise I would be looking at a salon, an A4 or 3-series.
EDIT:
Thinking about it the Audis are even worse than normal on this. So many times I see something in the review view or coming towards me on the opposite lane and I think it is an A4 or an A3 or A5 or whatever... then it turns out to be an A1. From the front I don't think I could tell the difference between the A1,3,4,5 or 6. It just seems to generic, too boring.