I use Wonder Under (Pellon 805) exclusively after trying many other brands, including those listed so far plus a few others. Some of my reasons asre:
It is easy to hand stitch through, even in multiple layers.
It never gums up hand or machine needles.
I can run it through my inkjet printer to get accurate copies of patterns.
I can transfer patterns directly onto the fused web so I don't have to dull my scissors/cutters by cutting the paper.
It's readily available and low cost.
It's the widest fusible web available.
It is consistantly reliable and, in my experience, never goes 'bad'.
Some tips and tricks on fusible web.
http://artfabrik.blogspot.com/p/fusing-tips.html