No liners.

The sock is part of the fit of the shoe - the thickness of the sock will let you tweak, just a tiny bit, the volume your foot occupies inside the shoe. I found that Smartwool socks the others mention are excellent; so are some Bridgedale trekking socks. They worked well with the Vasque Breeze shoes I used for a number of years. However, when I got my current pair of Patagonia Drifters, I found that the thicker wool socks made the shoes just a tiny bit too tight. I dug out some old Thorlo hikers I had, which weren't quite as thick, and the fit was perfect. They're also very comfortable for hiking. (Oddly enough, the Thorlos are 100% synthetic - no wool content. They do make a thicker, similarly-constructed Trekker version that does have some wool content.)