Do you like your SO's siblings better or your own sibling's SO?
I like my husband's brother, Ben, - we knew each other years before I met my husband and when I DID meet my husband, I didn't know he was Ben's brother. Anyway, we get along really well.
As for my brother's girlfriends in the past - I've hated all of them. Right now he's single but I hope his next girlfriend isn't a loser.