Rob, given the choice between a 172/Cup and a S3, I would take the S3. I have test driven a S3 so this is an informed choice and not because of some magazine review. At the time I bought my 172, the S3 was still out of my price range and given the money I had £12K OTR for a brand new 172 is bloody excellent value considering the equipment levels. As you point out, the S3 may not have as much space as a Golf, it does have more space than a Clio, is better built and has better driving position.
Don’t get me wrong, I’m a great fan of my 172 and always take the long way home and is a blast on twisty roads. However, being a turbo, the S3 can be easily tuned to 260 odd bhp with a £350 AMD chip. Now you’d have to spend thousands on a Clio to get that sort of power. I agree the Clio is really fun to drive and enjoy taking it on twistier roads, however, I prefer to drive faster on A roads as its safer due to greater line of site. On these roads the S3 will have the edge especially if it’s on a wet day. Therefore the advantages that the Clio may have on a twisty road is not that great for me but still great fun in any case.
On the track I would hazard a guess that there wouldn’t be a huge difference in lap times either. At the end of the day, I considered many cars but the Clio172 gave the best compromise for price, performance and equipment, but that’s not to say there aren’t better cars out there, my previous car, a Fiat Coupe 20V Turbo LE ( which is even faster than the S3!), gave me bigger thrills than the Clio.