Does anybody really base their decision on what kind of car to buy on the opinions of a load of people on an internet forum that they've never met?
For the record, I wouldn't have an M3 because they mainly seem to be driven through town centres at full chat in first gear by people who are old enough to know better (who may or may not look like drug dealers). But then I wouldn't have a GTA either. Partly this is because I'm too poor, partly because I prefer the 156 with no styling additions whatsoever, and partly because in most of the driving I do I don't utilise the full potential of my 2.0 TS so a GTA would frustrate the hell out of me.
If I had the time, money and inclination to do regular track days that view might change but I don't think I'd buy either of those (I'd buy a Volvo 960 Turbo or SAAB 9000 for the job, strip out the interior, and spend a bit of time and effort getting it above 300 BHP).