I don't disagree with most of the comments in favour of the GTS - I think it looks great with the darkened headlight surround and 'shadow line' trim. But in the interests of balance, the 'S' is also a great car in its own right.
I actually chose one rather than a GTS because it suited my needs better. I didn't want something that was too stiff-legged all the time, so it's nice to be able to switch into comfort mode around town when I have passengers. Also, I didn't want the even louder exhaust that would annoy the neighbours when I have an early start. The 'S' sounds great to me and is startling enough! It's also just as quick and, importantly, has the uprated six-pot brakes.
In short, it can cruise in comfort or turn much more aggressive and sporty at the press of a button. I think I have the best of both worlds....Or maybe I'm just getting too old!