I have always used 2.5", but have recently changed my entire method of binding.
I now do it the Sharon Schamber's way and she has an AMAZING tutorial on youtube for it. Here is the link:
http://www.youtube.com/watch?v=4PE0Yq9iGlc
I know it seems silly, but that glue has changed my life...hehehe. No more using clips that are always in the way that I never have enough of to do the entire quilt. Now, with the glue, I do the entire binding and then can hand stitch (or even machine stitch) all at once.
Love this link and hope you do too.
Suzanne