Both are great systems, in my opinion.
Active Autowerke has been in the business for many years, and has an enormous amount of experience in BMW forced induction. They manufacture quiet a few components for the E92 M3, and I'm a fan of their exhaust:
Eisenmann has been in the business of designing exhaust systems since 1987, and their hand made exhaust systems are unparalleled in quality and exclusivity. The exhausts are German made, and very unique in the market.
I don't think you can really go wrong with either one, which is why IND sells both.