With one page design we don't necessarily mean that the website consists only of one single page. It means that the website has a design that allows to display all the core contents on one page. Beside that it should be easily possible to add further contents separately. Only that way the advantages of a one page design can be balanced with necessities that might come-up in the perspective of SEO. For further details regarding „one page design“ and SEO see: SEO optimization for Parallax Scrolling Websites: Is Parallax Scroll Bad or Not?

With „best“ I mean 1) unique design/structure/approach 2) easy customization and editing 3) SEO friendly 4) fully responsive 5) offering some space for the most common contents and 6) using the newest technologies.