Few things I'm considering myself:
- I like the darker MacBook 12" in the stores, but I'm worried it's more because it's different and that I'd get bored with it after a while.
- After using a silver MacBook Air for years, I think that's the safer and more timeless color. I'll be using the new one for many years to come as well, and don't want to take the risk, especially with this new price point.
- I prefer the contrast between the black bezels / keyboard and the lighter casing on the MBP.
- Silver matches many of my silver gadgets, like the Magic Keyboard and (older, all silver) trackpad.
- I read in some reviews that the Space Gray version picks up smudges way more easily.
- I never worry about scratching the MBA, since they won't show as much (not sure how much of an issue that is with the Space Gray though).