I was wondering what makes string different if they are made from the same material? Like what make toxic string better than (in my opinion) kitty string.

most of the good string is polyester, one of the differences is in how many strands the string is made of, the thickness of those strands, the twist pattern, and probably the quality of the source polyester. Then you have the slightly more niche stuff like the nylon strings, but then I’d say the same things apply across different brands of nylon as well.

Really I just pick string based on price and colour. So bulk YYE is a good choice, but lately I’ve been looking into bulk Kitty as well.