I've driven all the cars i've mentioned (has everyone else here done so out of interest?) and my perception of the quality of the cabins is of course subjective but I never claimed it to be otherwise. And from the reviews I've read (which are wholly objective by their nature) it seems I'm not alone in feeling the A3 has a classier, more quality cabin.
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Out of interest I've had eight A3s since 1998 and three Golf GTi's and a Golf VR6. The interior of the A3 used be well ahead of the Golf but having now driven the new Golf and sat in a new A3 (but not driven yet) I personally think the interiors are of similar quality and I certainly do not consider the A3 interior to be 'streets ahead'. The design of the two is different and it's down to personal taste which you think is best. The A3 has the classier badge but nothing else.
As I have said before I have been driving an A3 of one sort or another continuously for 15 years and have loved every one of them but I much prefer the interior layout of the new Golf. Others will prefer the layout of the A3. At least we have the choice of two cars of equal quality with being available with the same DSG gearbox which is important to me.