I used to be on deviantART primarily, but about 3 years ago I dropped it because most people that I admired started migrating towards tumblr and instagram. DeviantART has really changed over the years (I joined it in 2003 and stopped using it around 2013), so I can't really give you a scope on that other than it's a good place to browse for art but maybe not a favorite spot for a lot of more well-known artists. Some have grown such a following there that they maintain their galleries, but the amount of really good stuff was in decline the last time I was there.
Tumblr isn't really built for art (there's some resizing nonsense that can affect how people see your art sometimes!) but the chances of getting seen are a little bit higher than other sites can be as long as you utilize the tagging system. Also it's kind of cool, because you can get people looking at your art who wouldn't necessarily look at it because the reblog feature makes it easy for people to just keep pushing your stuff to more and more people. I've garnered a lot of followers because I drew something, and then someone following me reblogged it, and then some of their followers reblogged it, and so on and so forth. But to be honest, it's not much of a gallery site unless you curate a lot and pick a theme that'll work with it. Some people have made it work.
Instagram is where a lot more fine artists I know gravitate and you can get people looking at your stuff pretty easily through the right hashtags. Twitter I haven't had much success on but that's a slow build kind of site, unless you do a follow for a follow thing.