For durability in a bed quilt, my binding is folded in half before sewing on, so I prefer joining the binding pieces on an angle. I find it lays flatter and you don't have a bulky "bump" in your binding. But when you are piecing a binding of different fabrics, joining the pieces straight is your only option. I usually press the seams open flat, then trim them a little closer than 1/4". Pressing is everything. If your quilt is for decorative purposes and won't get a lot of wear, you don't need your binding doubled and can do any method since you won't have as much bulk. Good luck!