I think this is wrong:
Provide the *better* default.
That assumes that there is such a thing as 'better' when really it's
subjective. X might be better for Fedora, Y might be better for Gnome
and either might be equally good for a user!
The default is what the users will see for the first time ans what
reviews will feature. It is the first impression and is important.
If there was a choice then the reviews would notice that, surely?
Would they complain more about being offered a choice than about
someone else's idea of the 'better' background?
I would be much more worried about first impressions of things like
Gnome Shell than the background. If we provide Gnome Shell by default,
will anyone even notice the background?