My preferred seam ripper is from Clover, the Japanese brand....they make such marvelous sewing tools. This ripper, either the round white handled one or the flat brown handled one (cheaper but with the same point and sharpness) has a small, sharp point that fits easily under stitches and a very sharp ripper section. When mine is new, I use it directly along the seam line, between the two layers, and it takes those stitches out like butter. It's great for releasing stitch-by-stitch as well.
Seam rippers are a relatively inexpensive, necessary tool that should be replaced often -- like blades and needles -- for best results and fatigue relief. I buy them several at a time from Joanne's and LQS when I travel.
Jan in VA