We do quite a few socks, mostly Nike Elites for guys wanting to color coordinate and for school's teams. Sublimation is the best route, here. When sublimation transfers to the sock, there will be small white voids between the ribs. When working with white or light colored backgrounds for the artwork, this is fine. When it's a dark color background, they are very prominent. There are ways to minimize the voids by doing a light stretch but still doesn't work 100%.
Transfers would work but you will more than likely have even more sever rib issues as the transfer is lying on the surface of the ribs. With dye sub you'll get a better reception.
One thing I'll add. You will almost never see them being stretched as if they are being worn. That's because most people are picky and will wonder why there are voids in the artwork. Seems like the people selling these are embarrassed or trying to hide the fact that they are not perfect. Just have to be up front with the customer that it is what it is. Here is a pic of one of our first attempts. After doing these a few hundred times our results are much better than the pic, but not by much.
