I was looking around at brush pens and was wondering should I get the Akashiya Bamboo Barrel Brush Pen, the Kuretake no. 13, or something else entirely? I have a pentell pocket brush pen and it's alright but fades in long strokes so I was looking for something a little bit nicer.

The Akashiya Bamboo pen has a bit softer brush tip than the Pentel Pocket Brush pen. I saw a blog post recently on it:
http://meghunt.com/blog/?p=60

You should check out the Lung Sketching Scrolls Blog. Alberto gives great insight into a variety of brush pens in a number of posts:

http://robotninjamonsters.blogspot.com/2008/10/brush-pens-collection-review.html

I think you could try the regular Pentel Brush Pens. They work well, and the tip is a bit more versatile. Personally I like them a lot. And you can control how wet or dry your line is by squeezing more ink from the barrel. It might not be as compact as some of the others, but it could be worth exploring. I hope you find something best suited to you! :D