Brocks Alienhead is great if you like loud.
They also put off alot of heat.
They make great power and are high quality.
Akropovic also makes really good power gains, and are of high quality.
They are very quiet with the baffle in, and have a deep tone with it out.
The carbon fiber muffler puts the majority of the heat out of the tailpipe. You can lay your hand on the muffler after a ride, with the engine running.
Any tuner can make paper numbers for you, but either pipe, properly tuned, will be a noticeable improvement over stock.
The Brooks will likely make a little more power.
If you drag race, and want every ounce of power, get the Brocks.
If you street ride, it doesn't matter.
As BLU88 said above, pick the one You like the looks and sounds of.
The 2 pipes are different, but either is a good choice.