what does best strategy for seo actually mean?

it means nothing, it's a phrase that sells. a proposal should say what they'll actually do: which pages they'll change, which keywords they're going after and why, what technical fixes, how much content, what kind of links, and what they'll report monthly. if it can't name those, that's your answer. for a small site the honest version is boring: fix crawl and speed problems, a title and proper content on every page that matters, a google business profile if you're local, and a few relevant links. anyone proposing more than that should be able to say why.