I use French double fold bias cut most of the time. I will do straight grain, but I prefer working with the bias. I do feel it wears better.
I particularly like it with stripes, love having bias cut striped fabric as binding.
Yes, I usually make too much and have some leftover. It happens. I use those leftovers on other projects and/or in different ways. But mostly I make too much because I am usually starting with either 1.5 yards of fabric which I know is enough for a queen sized top plus leftovers, or a yard which will work for a twin size. I could start with a more correct square for my fabric but I just don't want to worry my little head too much.
If I do use length or width of fabric, I still put it on continuously mitering the corners and using mitered joints and not butt joints.