I don't think there's a "best artist" in general, but there are really good artists for specific tastes. Really depends what you're into, for example I find zeblackballd to be one of the best monster girl/nightmare waifu artists out there, and on the other hand I think D-art is a very good artist if you're looking for anal/butt stuff, but at the end of the day it's down to personal preference, down to what art-style you prefer and obviously your actual kinks and such.