That's a tricky one! If you want the complete Sonatas in one set, then Hamelin is your man. Sudbin seems to be slowly recording all of Medtner's works, so, if you're patient he would be the one. Kholodenko plays with amazing passion and power, but Delos' sound is oddly boxy and dry. I think they licensed it from some other source, as their recordings usually sound very good. BIS always provides excellent sound, so that's another point in Sudbin's favor. He, too, plays with great passion.