I don't know which is more popular out of FB and IG, but IG is fairly new compared to FB and FB is the parent of IG.
I remember hearing on the news that FB has a lot of fake accounts, dead accounts (including those of dead people whose family members have a hard time getting removed) and "deleted" accounts that aren't deleted, so it's definitely serving an "inflated YouTube views tea."
FB is probably bigger, but ultimately "everyone" must have an Instagram to be cool.