S5 really is a good looking car, but then so is an M3 which is why I bought one for 24 hours. If you need a one-car solution, then I would find it very hard to look past the M3 tbh. V8, four seats, boot, plenty of tuning options, V8... Complete package really.
That said, £25K gets you into a 997 as well. Ignore the mileage, it'll still feel fresh if it's been looked after, and you'll have £6K as a slush fund to fix any bits that go wrong. Colours aside, I think that's a bargain.