First of all, all comment sections I have ever seen on blogs are nofollow links so they are really a waste of time in terms of SEO, in terms of driving traffic they are ok.
Spend time writing quality over quantity content, but more importantly when writing it have a list of news sites / blogs / contacts in mind who you are planning on outreaching the article too.
The hardest part is the outreach, anyone can write a great article, but you need to get it picked up and distributed. In an ideal world, you would all ready have made contact with the journalists before hand and see what articles they want.
IMO journalist are very busy and if you can provide them with a great article which happens to include a link to your site, if they are rushing to hit a deadline, then you have a higher % chance of it being accepted on their site.
Social media the way to go: depends on what industry you operate in some industries this could be a complete waste of time. Especially if you are a B2B company. Plus with Facebook's latest algorithm update its actually quite hard to get a social media post in front of your audience.
Biggest tip would be, quality articles over quantity and spend as much if not more time on outreach to relevant blogs, websites to get your content picked upto and linked to.