I LOVE my seam ripper. It is the one with the surgical blade.
http://www.nancysnotions.com/product...hole+cutter.do
I change the blade once in a while. I haven't found anything that I like better. And it was confirmed how much better it is that the 'regular' ones - I had to take out a very LONG seam on a gathered skirt for a princess dress. The real issue was that one fabric was satin and the color was sheer. I had perfect control and did not cut the fabric instead of the thread on any of it.