Cant go wrong with either. I had an RPI setup on my M3 and loved it. RPI makes some good quality products. I chose Meisterschaft for my M5 because they offered the remote valves which was important to me. I absolutely love this feature. Oh, and the 102mm tips dont suck either. Sound is similar for both systems and I would bet the power increase is similar as well.
21" DPE Super Concave, Meisterschaft GTC w/LXR midpipes, BMC filters, Charcoal delete, H&R springs, IND cosmetic pkg, M-Performance Spoiler, Wrapped roof, Hardwired V1, Coded
2013 X6 50i MSport
2008 SmartCar - 2012 Wrangler Unlimited