One of my friends has a Ginger - loves it for slicing down a long seam, but says "be careful" she sometimes cuts the fabric along the seam if she is going too fast.
However, another friend swears by her 'Eyebrow shaper' from a local drugstore. It isn't as sharp as the Ginger, but she says she has never cut the fabric along the seam she is riping out.
Guess it is what you get used to using that makes it the best or not.