Preferred SEO Strategy?

Focusing on quality content and relevant keywords has been my go-to.

Actually, you should combine all these strategies to be successful. But the most weight I guess has the backlink building.

All of these are required to improve your ranking on search engines. You can't ignore any of these.

Before you jump on the bandwagon for backlinks, your on-page has to be in tip-top condition along with your technicals which partly helps for mobile friendliness. But most ditch the on-page and start looking for loads of backlinks then Google takes an interest for the wrong reasons.

Keyword research, On-page optimization and quality content is pretty much all you need today. If your content is adds value other sites will link to you organically.

I can't see how anyone wants to rank sticking to only one or two of these strategies. They're all important and none should be underestimated.