I vote SK over Williams. Williams seems to source more and more of their tools from overseas every year, so much so that is becoming a bit of a hunt to buy American made tools from them. This leads me to believe that Williams will become what Craftsman tools has, and if you need to warranty your American made tool you'll get the Orient's finest in return. SK on the other hand is devoted to American manufacturing and takes pride in their name. I have SK impacts, ratchets, wrench, etc. and I have the same in Snap-on tools too; at the end of the day I've never had a Snap-on tool do the job my SK tools couldn't or vice versa. I actually prefer SK impact sockets over Snap-on's, and SK x-frame wrenches are excellent. SK also has semi deep sockets, so they can fill that niche for you as well. Buy the SK pro membership, and you can get a nice socket set for the cost of the membership over the course of a year as well. I did that and have another 1/2" drive shallow socket set from 10-21mm, and cost me $20 for it (student discount was used for this).
On a side note, I'm a student currently and have wrenched professional prior to my education. I have used a ton of different tool brands, and I am still acquiring new brands as I learn more about various manufacturers I haven't been exposed too. As I've learned more, the more I tend to be less concerned about the brand name on the tool and more concerned with the quality and functionality of the tool. With that said, Snap-on has lost a lot of luster to me as a whole. They do make some tools that are topic the mark (i.e. hd gold torx bit sockets), but others that are average at best (i.e. cordless tools). Do your due diligence, and you'll likely be satisfied with your purchases.
Another friendly reminder buy Koken sockets, especially their zeal line. I consider them to be the best I've used, and they are fairly cheap. The only sockets I'd consider "better" are Nepros, and only because the finish on them is unreal. In use, Koken and Nepros are equal and I'd opt for Koken because they are much lower cost than Nepros.