Pay Google or a Marketing company?

How do you manage Google SEO to improve your business's visibility? Do you prefer paying Google directly through Local Ads, PPC, or other advertising options they offer? Or have you had any success with the countless agencies that promise to rank you higher on Google (and seem to call all day)?

There are so many options out there, and it can be hard to figure out the best way to advertise. Everything seems Google-driven—you either pay an agency to handle SEO (which ultimately pays Google) or try to manage it yourself.

Any suggestions or advice would be greatly appreciated. Thanks in advance!