IG is nice, especially if you do a lot of traditional work and sketches. IT's great to share WIPS and share your life with people (though some people don't like that).
However you need a special program to upload from your computer, and it's pretty much mobile only. IT's hard to get a following and people are very bad, worse than dA about commenting.
I personally love IG since I do SO MANY sketches and WIPS that it makes it easy to share and update my following so I don't appear dead.