This will sound a bit daft seeing as I own an S3, but while I was waiting for my car to be delivered I had a lot of people says stuff like "oh you'll like the nicer interior over the Mk5 GTI" etc. At the time I didn't really appreciate the difference and dismissed such comments. Certainly, the interior was not one of the reasons that attracted me to the S3. Indeed, ergonomically, at least, it is inferior to the Mk5 in a few ways. However, after owning the S3 for almost a year now I do admit I much prefer its interior over the Mk5. And while I haven't spent a lot of time in a Mk6 to get a proper feel for its interior I dare say I'd still rate the S3 ahead.

Having said all that, Golf interiors, esp since the Mk4, have been first class and IMO anyone who used the interior as the only reason to buy an S3 over an R or even a GTI would have to be living in la la land, haha.