I would think it would be hard to name a specific width of binding that works perfectly for all quilts, every time. The fabrics and battings make it hard as each quilt is a slightly different height. Treatments like serging the edges, sewing the edges down, etc. all will make a difference in the height as well.
Therefore, I'd seriously consider sampling different widths of bindings on each quilt before cutting it all. I'd make several samples, 2", 2 1/4", 2 1/8', 2 1/2" widths, etc. To test them, I'd pin the binding down for the 1/4" seam, pinning as if it's a sewn line, then wrap it around and see where it landed and where the top seam line would fall or where it would need to fall. I'd find the best one that fit, and if you like it, then proceed with that width, and you'll already know the exact seam allowance to sew with.
I'd certainly either pin or glue the binding down before sewing, to make sure it's in the right place. Since you've already tested the width, you'll know the exact seam allowance to sew it with.
This is the only way I can see it working perfectly, all the time. Clear as mud?
Hopefully, someone else knows better than me...
Debbie in Austin