Facebook is of course number #2
Why?
Well, when you think of social pages, Facebook is one of if not the first that you think of. Facebook is an easy place to share content and get feedback fast. Also with the FB like page that you can create it can separate your personal account and business.
One tip when using social media
NEVER, use all of them the same way.
I am guilty of this and I have started to stop doing that.
With Facebook, you don't want to post as often as say Twitter or Instagram (if you use that). I would say that once or twice a day is good enough.
Also another tip is, yes you can post the same content more than once,
BUT it needs to be done in a specific way so that your followers are going to think that you are spamming them.
Read this article to see what I mean. :)
https://blog.kissmetrics.com/double-your-social-me...
Anyways,
With Facebook, you can write a longer message with your content than twitter, but I wouldn't suggest making it too much longer.
Also, as the article says you would want to change your message up with each blog you release. For example sometimes you might want to include a fact with the URL and sometimes you should include a snippet of the content itself.
Facebook is one of the biggest websites ever only really being beaten out by Google.
So if you are stuck wondering if you should promote through facebook then just hurry up and create a page now because yes you do.
In my opinion, when using Twitter we need to do regular tweet almost twice or thrice a day (compared to FB or Google+) because of its short content and twitter timeline is ... what they say, "jet-pumped".
Other new tweets will come to my timeline in just few seconds, so I think we need more tweeting to make our follower realized that we are active in twitter too.
That just my 2 cent :) Oh, thank you for mentioning Youtube. In the training, we were taught to use mainly the FB, Twitter, G+, and Pinterest. Maybe in near future I will try to create my youtube account :)