I was taught that bias really lasts longer that straight grain because there is no just one thread at the edge, it is a criss-cross of many threads. Frankly, though, I have not had a particular problem with binding wearing out even with quilts I have had for many years. And it can always be replaced if necessary. SO, I do bias once in a while, or on curves, and mostly use straight binding myself. There is a cool technique to make a bunch of bias in a really easy manner, but I have sort of forgotten how.... You probably could search for it or someone here would know the technique.