The sk vs snap on is really apples and oranges in alot of ways. If you need an open end, you should look at the wrench for the open end (snap on is very good here); if you need length, look at the wrench for the length (again, snap on). If you need short, look for a wrench with the correct shorter length (like sk or proto/facom/stahlwille). If you need nothing to do with open ends, look at brands that offer ratchet/box (like snap on xdhr) or double-ratcheting box (like facom 67 series).
I don't really consider snap on and SK to be substitues most of the time. If you need snap on, grab it. If you don't need snap on, you grab whatever is the correct tool (and there is alot of competition out there). Some people don't like certain ergonomic profiles, and some people need different shapes for different parts of the wrench (thick, round handles for pulling heavy torqye, thin/flatish handles for flipping over using 15 deg open ends).
That is why there is lots of differnt niche brands out there people like.
Arbitrarily picking 2 brands out of thin air is sort of a false choice.
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SK isn't exactly quick at bringing new product to market.
