And now it's time for a little bias to come out. Instagram and Google+ are completely free. There is, in fact, no way to pay them to modify your experience in any way. That makes them entirely level playing fields. Facebook, on the other hand, is proffit driven and wants nothing more than all of your money. Yes, all of it. Facebook pages used to be a nice thing. Facebook used to show your posts to all of your followers. The operative word there being, "used to". Then they figured out that they could charge you to reach all of those followers you worked so hard to cultivate. Once they figured this out, average post viewership dropped from 90%+ to about 30% unless you pay them to sponsor the post. As a small time artist with no advertising budget, this is highway robbery.
In short, I don't use Facebook to promote my work and I don't suggest you do either.