Well since people picked Instagram possibly from it being their personal preference because they use it more, it's truly Facebook that still has just a bit more popularity because we can't forget the numerous adults i.e. Parents, grandparent, etc. that still use Facebook. I'm not saying they don't use Instagram, but it's more like that they use Facebook first since it's accessible by computer and adults use that more easily than mobile phones. And other reasons too.
But in my opinion, I like Instagram better 😋