I'm a backlink nerd. I spend about 4 to 6 hours a week analyzing websites and their backlinks and then analyzing those backlinks to see where they come from. I typically will only analyze the first 5 to 10 websites that rank for a keyword. You know what I've found. 98% of the websites at the top of the SERPS uses some directory links, guest posting, curated links, footer links, profile links, and guest posts. Every one of those types links will move the needle. Some more than others obviously. The trick is getting a diverse amount from each source. If all you have are the same type of link, it's a dead giveaway. Mix 'em up.