You should try to use and offer the communication channels where your target audience - user and developers - resides. This might be the same channels, different ones, or there may be a certain overlap.
You do not want to force any of them to use one particular channel, especially if they don't like it. But you do not want to force yourself to use an channel that you are not comfortable with, either.
Within the GIMP project, we have two main mailing lists, one for development topics, one for user topics. There is also two IRC channels, one for mostly development topics, one for user topics. We also monitor Reddit and G+ and Twitter to some extent, but this is an effort done by individuals.
I can't tell anything about whether we are active on Facebook - I have an account there, tried to use it, but couldn't because there was too much data I perceived as noise, and that was without following anyone.
Web forums are done by third parties, without too much involvement from anyone of the core group. This turns out to be a problem sometimes - if I ever want to learn something I never knew about GIMP, or an esoteric reasoning for some GIMP behavior, I read those forums. But the amount of unverified and speculative information there also prevents me from subscribing - I'd probably be banned within hours for being "too negative" for all the "no, this is not quite correct" replies. This is a complaint that happened to someone from the inner circle when doing just that.
So, lesson learned there: if you want to have a forum for your application, you run it and you make the rules.
I am the admin for one of the forums, and I leave users there pretty free reign (I stop discussion when they get into ad hominem space, though). But recently, I found myself having a lot less time to check up on the posts - and found the same speculative creep starting there.
Lesson learned: if you run one communications channel, make sure that you keep control of it.
Overall, my personal favorites are mail and IRC. I know that these feel antiquated to many users now, but I do not see myself using anything else comfortably.