I have huge feet, 12 or 12.5 shoes and 4E width, so it was an almost pleasant surprise when the XL size was a bit bigger than I expected for my feet.  I like my socks to fit rather right for athletic performance-type socks, so if you have feet like mine, Large is probably the size to go with.  Performance-wise, they are very comfortable and wick moisture away from the foot very well.