2.5

Looks like I'm in the minority but I cut mine 3 inches. I like a little wider binding.

The cut width depends on the width of your seam. for a folded binding start with 6 times the width of your seam and adjust accordingly. However that formulae doesn't take into donsideration the folds of the binding both when you fold it initially and the fold to the back. Since most of my quilts have a 3/8" seam allowance I cut 2.5".
When you initially stitch the double folded binding down, then measure how much binding there is to the left of your seam line. It should be slightly more than twice the width of your seam. I found 2.5" a little wide so started cutting to 2.14" and it works better. I attach the binding to the back by hand. The seam of the binding should be consistent and a size to fill with the quilt. Practice a bit until you have found what is good for you.

I use 2.5 for quilts, 2.25 for wallhangings. It is a matter of preference for everyone. Whatever you are comfortable with and works for you is what you should do.

2 1/2" and fold over to make it double. Sew on with 1/4" seam. I only quilt with Warm and Natural or Warm and White....

2" works for me unless I'm using a thicker batting (I usually use Hobbs 80/20). I use a 1/4" seam to attach it to the front. If I use a wider seam allowance to attach it, then I also increase the width of the binding.

I cut mine 2 1/4". Turns out perfect every time. :D

2" folded over and folded again, giving my 1/2" of finished strip on the quilt.

2". The tighter the binding, the longer it is supposed to wear according to Kaffe Fassett

I've been using 2 1/2" folded in half, but I'm going to increase it. I like a slightly wider binding.