pds41: I bought this game from GoG. I'm happy that I bought this game from GoG as I want to support the developer and I like the principles that GoG stands for - DRM free and classic gaming on modern systems.
Careful. Rarely does the money from GOG reach the developer, especially for old games. It's usually pocketed by a licence holder, and that's usually not even the original publisher (see all the Activision and EA titles here). With SW, that might not strictly be the case, as 3DRealms seems to still be in a position to control some of its properties, but then the question becomes who from the original devs is left there, and do you really want to support a company with as shoddy of a recent record as 3DR. Just food for thought.