I have both the Proto and the Snap-on in 1/4". The Snap-on is about 3/16" of an inch shorter. Both work essentially the same in operation, I don't notice much difference in angle they will work at. Given that, I'd give the Snap-on a slight advantage. It's also 12 point, which gives a slight advantage in getting the socket on "just right" to give the most leverage in turning, as a slight angle can make a difference. Some guys might give the 6 point a slight advantage because it's less likely to slip if it gets on crooked. So, kind of a preference or situational thing there. The Proto 6 point is just a slight bit thicker, so won't fit into as tight a spot.
Overall, when I went to buy a set, I looked at the Proto price difference, and bought a complete set of them for about 1/4th to 1/3rd the price of Snap-on by waiting for coupon deal at Zoro. I already had a few Snap-on singles; of course 10mm is the first one to get.
My swivel sockets across the three drive sizes and metric and SAE are about equally split between Proto and Snap-on; and I have overlaps in the brands. In use I don't differentiate between them and use them without preference.