Let us know how it works out and which one you find the most effective and efficient...

Of these, I would recommend Quora. It's a question, and answer site. You can post answers to topics you have knowledge about, and put your related website url with the answer. This can bring you free, targeted traffic. Affiliate links are not allowed, only website urls. Good luck, Tom

Reddit is very restrictive in many subreddits, it is completely pointless in my niche. I have 5 subreddits of my own and cannot add my own stuff there any longer, they warned me that I was overusing the medium. Some subreddits do not allow any link at all, so how you can have traffic? Better forget it.

But I think you missed one which is in my view the most powerful, see my trainings. This would bring thousands of visitors in one single day. Unfortunately it stopped working at my side, bit it does not mean the same will be for you, so try it: What is flipboard and how it works Flipboard development

There is a complete listing of social media sites (including some niche sites like Taltopia (actor's community) on Wikipedia. Just query 'top social media' sites for a listing. I've got accounts (mostly to protect my brand) on over 50 sites.