Correct me if i'm wrong, but when it comes to seo, I don't see anything other than PBNs being relevant anymore. Let's see, the GSA style backlinks were scrapped long ago. Link wheels etc, pretty much useless. I pretty much have ranked all my low-medium comp keywords with PBNs only. I used social signals and blog comments ONLY for diversity and to make the link profile look natural. But my rankings really only came from powerful PBN links usually takes 15-25 to rank #1 for a medium competition keyword. Guest posts, out reach, stuff like that is very slow and hit and miss. Sure it may help if you can manage to get a MAJOR site to link back to you, but the likelihood of that... is low. And the returns are really not guaranteed. Plus it is way more work than any other method, and much slower. Web 2.0s, they sound nice in principle, but link juice is a real thing. And freshly made web 2.0s carry virtually no URL link juice. Thus they have virtually no effect on SERPs. Unless you add thousands of pages of content and redirect to web 2.0 home page. Just to rack up the PA, but then again, that is also quiet a slow process (unless you have a bot) and still not as powerful as a link from a high metric aged domain. Social signals, shares etc... I've tested it and they have a marginal effect on rankings. May help indexing too. But its so minimal that you would hardly be able to spot it within the natural serp fluctuations. This really only leaves PBN as the link method that can reliably return results... Tell me if theres anything else.