Snap-On and Williams are made and distributed by the same company.
A couple of my Williams socket sets were delivered with Snap-On sockets on the rail. An odd size, like 11/32", I think, in one case. I reckon they were out of Williams in that obscure size, and just made the substitution.
There is nothing "better" in the steel, manufacturing tolerances, or functionality of Snap-On over Williams. What is better is the convenience of the truck distribution and warranty process. Sure was nice having the Snap-On guy show up at my workplace* many years ago. Walking through that truck full of gleaming new tools, and being able to buy what one needed was just awesome.
*I spent a couple of months working at a junkyard, in Bloomfield, CT, during the time I had off between college graduation and starting AOCS in the USN. It was a great place to learn about cars. We pulled them apart, setting aside engines, transmissions, steering columns (tilt was rare back then), good body parts, including glass, and interior parts that the owner thought would be valuable, or that were satisfying an order for a used part. I got a used 350 Olds engine from that yard for my '77 98, for example. I never did buy any of the Snap-On tools, I was saving up my $$ for my new career and couldn't justify the cost of tools at that point in my life. But the guys I worked with would get something off that truck every week. It was fascinating to watch the business model: payment/installment plans, product sales, service. Sure was attractive. Sure was expensive.