My favorite is small, blue and round. I think it's this Dritz one:
http://www.amazon.com/Dritz-3-1-Inch...dp/B000Y3ESWE/
The ripper portion is fine enough to get under very small stitches, and it feels good in my hand.
There is a new one on the market that has a rubberized end for getting rid of the cut stitches. Have seen very positive reviews about it. Don't have a link, but maybe someone else will post one.