^^I like the little ones {called bullets} personally as I can't stand the way it looks to see a plastic disc behind the ear of fine jewelry.
like these:
My studs are a full carat each and don't pull forward at all, maybe because they're martini settings{?}
They do have the discs as well though, I know people like them.
like these:
I like them because they're SO much tighter than the metal ones {friction backs} that come w/ earrings, you really have to work them on, there's no way they'll slip off accidentally.