Do u think that you could simply Google "worst SEO company on earth" ?
Or would that be too simplistic?
In a sense, they can't be worst if they come up in the top of Google search.
Worst SEO company would probably be something that is just had its inception.
Though that may not be potentially worst. It depends on 'worst' in exact what ways.
Like, one can say a newly starting company is worst because of lacking much resource, clients and stuffs. But the founders or workers may be talented enough, and they might have built a rich environment conducive to growth. In contrast may be some more established company as worse than that for their inability to keep up the business or something like that.