I think there's no such thing a a "typical" settings file on Linux!
I just did a quick survey of 20 .conf files in /etc on my debian system, and found:
1 file used "key value"
5 used "key=value" (actually, a couple were "key = value", allowing whitespace around the "=")
14 did their own thing.
The 14 that did their own thing were all over the map; from one-value-per-line to "key:value" to full-blown XML. # is
the universal comment character in the Linux world.
My vote would be for:
# comment
key1=value1