I don't think they sound necessarily "better". 9s will give you a thinner tone, but it's easier to bend and in my own experience, they last a little less than 10s. 10's are a little thicker sounding, a tad harder to bend at first, but you get used to it. I have been using 10's for 7 years, then for 1 year I switched to 9s and I couldn't consider it "worse".