ya, its mostly come up to personal preference. I have the magnaflow because I won it in a contest and I love it
Both are similar price wise.(magnaflow mostly cheaper in general)
The BMW PE is more high pitched sound, which many prefer while the magnaflow is more low deep exhaust note. That being said, the magnaflow is louder then BMW PE. The BMW PE is just an axle back, while the magnaflow is a cat back.
The magnaflow should have better "power gains" because it is cat back, but who really knows, and if it is, it wouldn't be a lot much more.
Edit: Here is a video of my maganflow. I recorded it with my iPhone camera. Sounds louder in person, but you get the idea. I also only revved it to 3.5k.
and one of BMW performance