I have now had long enough with a Magnaflow and Borla on my MCS
to get a feel for how they compare.
First the sound... the Magnaflow has a great aggressive sound but a loud drone on the highway - loud enough for me to swap it out. The Borla is very quite - at idle you can hear a deep rumuble but there is very little extra sound at other speeds. I subjectively put the Borla at 150% the volume of stock and the Magnaflow at 300%. There is absolutely no drone from the Borla.
I have a GTech/Pro Comp and thought it would be easy to compare the power - it wasn't. When I added the Rogue CAI, it was easy to swap the stock intake in and out until I got stable readings and be confident that I was measuring a 7hp increase.
I measured the power every day at the same point on my trip to work to make sure the engine temperature was consistent but still got variations. The thread on heat effect on power suggests there is a 1hp loss for every 3 degrees F which helps explain the variation. Based on lots of measurements, I am pretty comfortable saying the Magnaflow got 10hp and the Borla gives 5hp - that's on top of the 7hp from the Rogue CAI.
There's nothing really new here - get the Magnaflow if you want maximum power or maximum attitude. The Borla is a good fit for less power with a quiet ride. The problems I had getting consistent power measurements makes me doubt the accuracy of tests based on a single dyno run.