Dynamic sites can have lots of "meta" (non-content) pages or pages with duplicate content, which can be very bad for SEO. HTML sites are also easier, at least initially, to create.
Simple static sites can be easier to manage in some cases. It depends a lot on what you are trying to do. I often prefer static HTML, if I'm not going to be updating a site often. Even then, I don't just write HTML... I use HamlPy and Django templates to produce a site and then I mirror it with wget, and upload the mirrored site to my hosting.
This question already asked lots of time . find here complete answer.http://forums.digitalpoint.com/showthread.php?t=2526393#post17894913
There are SEO pitfalls using a WordPress blog; duplicate content issues, wp-content crawls, category pagination and so on. Getting familiar with Yoast's WP SEO plugin can help with them, if you know what you're doing. For some people it's easier to just set up a simple static site.