My close friends always get Admin or SuperAdmin. I've got about 3-4 SA's and 3-3 A's.
Although, it's worth mentioning that 3 of my SA's I know from IRL and am close friends with.
My Auto-Admins usually are very close friends on the game, or people who I can really trust and have been on my server for fair amounts of time, usually are regulars and I know that I can trust them.
Otherwise, I tend to give Admin occasionally if I'm bored and no-one is on my server and one person joins and I have nothing done. Mainly cause I like to see what people do, also, some people will load up builds of theirs which I can use on my server with them and have some fun.
These sort of people generally turn into closer friends, oddly enough.