I'd like to hear what your experience is in this matter, but here's mine.
I've grown weary of Facebook. Whenever I post a bit of art there, some people add a like, but hardly ever comment on it. Here on DeviantArt I almost always get posted replies that lead to interesting discussions, or at least duels in clever punning. Nor do any of my Facebook posts go anywhere. They just sit on my own Facebook page, and they never lead to any opportunities, or any new and interesting contacts. I frequently find my DA posts popping up in Google image searches, and a few times I've been contacted by people who want to use my art (and pay for it) because they found it posted on DA.
The only reason I'm still on Facebook is because I'm managing an account for my dayjob, and I'm currently involved in a project that will probably necessitate the use of a Facebook group.