I own bags from both companies as well as hop socks and dry hop bags. From my experience, both bags are excellent. The brew bag seems a bit more heavy duty from the perspective of the seams, and after 30+ brews, shows no signs of slowing down. The Wilser bags appear to be great quality as well...
A little late to the party but just wanted to give my 2 cents on the Brew Bag. For me, and I do not have experience with the Wilser, the Brew Bag does a great job of keeping the spent grains out of my wort. The straps are actually helpful as well because when you attach them to a pulley system...