Static html or Wordpress?

I found some static html site ding good on google, they are mostly old website.

Also which way is better for SEO: use free blogs or have my own domain name?

Your own domain, you have total control on your site.
Use WP, choose the right plugins to act as static html (at least for the output).

They're doing good because of the domain age and number of backlinks.
Static html and WP doesn't differs much.

One of the advantage by using WP is having RSS to publish.

As for own domain / free blogs?
I found that it's easier to promote free blogs aggresively and harder to get banned by google.
Own domain has it's own advantage especially for the long run.