I used to ask this kind of question before. While I was waiting for the reply, I headed out to seek for the best recommendation and advices from the programming and SEO community. My main intention is to know which one is better in term of SEO.
While there are many debates and different perspective, the majority of people who know what they're doing and know what they are experimenting are giving the same advice.
WordPress is easier for us to manage our site as well as many functions and plugins which could be possible to do various jobs on it. Static is harder to manage, but it's more scalable than WordPress because it's just static and could produce more functions with the hands of expert.
The final result is the same because both static Html and WordPress sites will produce the source codes for robot or search engines machine to read. The sources codes are still a bunch of markup of Html codes. Therefore, their is no real power of SEO of which one over other one.
In contrast, there are another factors which could lead to the bad of ranking such as site speed, bad markup by using not valid W3 standard or using iFrame etc.
Therefore, there is no debate about what is better than another in term of SEO. If one could manage and optimize their WordPress sites wisely, their sites will have better rank than the old dated error static Html sites and vice versa.
There main point that static Html is better than WordPress is the speed because they don't need call more queries from databases and only static files are reading by Search Engine robots; therefore, it's faster than the heavy coded WordPress. Even though this is better than WordPress from the start, but if one does not code their static Html sites wisely by adding bunch of codes that is not really neccessary, their sites are also slower than someone who optimized their WordPress sites wisely with good hosting provider, too.
Like some comment above, it's depend on which one you're comfortable with and which one you prefer to use. For smaller site and rarely to update or edit the content, I prefer normal static Html structure. Yet, for heavier and easy to add more content regularly, I'd prefer WordPress.