I have a Quaife and here's what I like about it:
-Proven technology. Been around for decades
-Quiet. No difference vs. stock in this regard
Can't comment on the Wavetrac. But the Quaife - the dependability of these things is worth a lot.
2011 BMW 335i E92 - Le Mans Blue, 6MT, M Sport. JRZ RS Pro, Quaife LSD, BMW Perf Exhaust