Right now Steemit most definitely dominates my social media habits just because there's so many possibilities and projects that could stem from it. It feels very versatile in its current form.
I do use facebook still (even though I am not a fan anymore) but its my connection to my friends and family, and its a great way to turn people onto Steemit!
As far as other social platforms go, youtube is oversaturated for video content so I only use it for hosting my videos. Snapchat could be useful for promoting steemit posts and such...
I'm not sure discord would be considered a social media format (its more of an instant messaging platform), but I do feel that it does have a HUGE value in supporting social media through community building and person to person interaction.
Great post here @firepower. I was recommended here by sir @whatamidoing :)