MPE or Akra......my 0.02c
Personally, I like the Akra, however decided to go for the MPE, as I wanted an OEM part, and preferred the sound, but sound is subjective to the listener, so that's your call. I will say this though (and it's probably more noticeable to me as I drive my car infrequently) the MPE sound has improved over the lat two thousand miles. I have heard this from other members, the sound "matures" with use, it actually sounds better over time than when new.
Another consideration for me was the "authorities". Where I live the police presence is intense, simply put there is a cop about every three miles, and these guys are aggressive and heavy handed. I am an old dude, most of my town is 35 or 25 MPH speed limit, and I use cruise control in town, all of the time, to avoid any type of police harassment. I will bet that any day now I will be pulled over because the MPE sounds magnificent when pulling away from a traffic light and getting into the revs a little. The fact that the MPE clearly has BMW stamped into the muffler tips will save my ass, as it is an OEM part, and the cop will not be able to harass me for "aftermarket muffler noise". This car is enough of a cop magnet, without making it louder, so consider this too before making your decision.