I've got the Active Autowerkes exhaust. Don't listen to anyone who says it drones. Most of the exhaust systems on our cars cause a tiny resonance that affects the rear center console that can be easily fixed. The sound I think is a perfect mix of performance and comfort. I drive on the highway a lot and don't have any issues whatsoever. Just be sure to fix the rear center console theres a DIY for it somewhere.
1997 M3 Coupe - BMWCCA I-Prepared #22
2006 M Roadster - 23,000 miles and slowly counting