To be honest, you probably don't need either one to learn how to make socks because there's so much great free info on the web. That said, if you're going to choose one, hands down it should be SKS. No contest at all. Socks Soar is a skinny little book that when you see it you think "Is this it?!?!?!"
(I was very glad that I borrowed it from the library because I think I would've been mad if I spent actual money on it) whereas SKS is jam-packed with all kinds of good info, including
how to do socks on two circs. It also offers many different options for construction and offers a nice array of stitch patterns. A second book, "More SKS" is supposed to be coming out soon, BTW.
I've also read good things about Queen Kahuna
, a self-published offering that's supposed to be very detailed and repleat with pictures. I've never had the fortune to lay eyeballs on a copy as the $25 price tag turns me off, but it might be something to consider. (If anyone has it, please let us know if there's anything in it that we can't find elsewhere because she claims to have these valuable secrets, but I suspect they're not all that special.)