I had to return the small size because it just wasn't quite right.  Because of the liner, they fit a little awkwardly.  I wear between a 7 and 71/2 in womens sizes so for me it was a tough decision between the small and medium.  If you are between sizes, I'd recommend going with the medium.  Because I am returning them, I didn't test them in the water to see if they did keep my feet dry.  I haven't tried any other waterproof socks in the past, so I can't compare their thickness, but these are not much thicker than my regular hiking socks, so they would still work fine in my regular shoes.  I will also say that they don't have a lot of shape in the arch, so they don't stay close to your foot if you have a high arch like me.  Finally, I think it is just the way they were folded in the packaging, but I had a sort of crease down the middle on the top and bottom, but it was more prevalent on the bottom.  This would hopefully work its way out, but was a little uncomfortable.