After more years sewing than I care to count, I have settled on the extra cheap ones from jhittle.com. I almost never cut a whole bunch of threads at one time. If I have a whole seam to do, I cut a thread here and there then pull the opposite one out. Besides being cheap, these blades are very slender, so they go in easily. I treat them like sewing needles, planning on regular replacements. When I go to a guild retreat, I have extras to hand to friends. When my beloved decides to use a ripper to pry something nasty, I can be gracious and say, "Oh keep it, darling."