OK, so this one’s kind of complicated… just kidding. SEO stands for Search Engine Optimization. You engage in SEO when you attempt to get a page to rank higher in a search engine’s SERPs (search engine results pages), with the ultimate goal being to increase organic (unpaid) traffic to that page.
This question is a little like asking: Who’s more important to the Patriots, Bill Belichik or Tom Brady? You can probably come up with an argument for either; but the reality is, both are vital to the team’s success. The same goes for SEO and PPC (pay-per-click). You couldn’t establish domain authority, organic brand affinity, and really, a wholly formed online presence without SEO. By the same token, you couldn’t granularly target prospects by demographic, behaviors, or keywords without PPC.
Again, you could come up with a good argument for a few different answers here. Ahrefs is great for competitor content and backlink research; Moz Pro’s content explorer is great for finding unlinked mentions; and SEMrush is great for rank and visibility tracking. The three share many overlapping features. It’s more a matter of preference than anything. Spyfu, AWR Cloud, and DeepCrawl are also worth checking out.