i haven't found any reliable way to separate good and bad triangles...the sinker floater trick might work sometimes, but it's still not very reliable. you'll still get some crap sinkers and good floaters. probably the only way is to get a really good, expensive durometer. i have found though that buying the 15mm size of triangles and also le pros yields much better quality tips overall in the box. not sure why....the 15mm tips are also a bit thicker, perhaps they come from a different/better part of the hide?
the OP mentioned a good single layer tip, black diamond....i think the OP means diamondback. they were colored black on the outside, but inside was very similar to a triangle. IME, they were very consistent from tip to tip, like getting a perfect triangle every time. unfortunately i believe the company went under. if anyone wants some, i have a small stash left over, PM me.