I have both versions of the Borla cat-back exhaust (I have 2 Cooper S's, in the US and in the UK), and I prefer the non-Sport version.
Non-sport: Nice popping sounds and note during spirited driving, but quiet during highway cruising.
Sport: Very nice popping and great note, but it never goes away, even on the highway cruising in 6th gear. Gets annoying after listening to it for hours, especially if you have a sun-roof. But, very fun when driving around town for short trips.
This is the sport version on a wet day on a cold start:
http://homepage.mac.com/gskoglind/.M...ortExhaust.mov
My preference is the Non-Sport version.
