Do I need to use a web framework for a simple website?
It depends on what kind of website you are planning to come up with.  If the website is going to be just a set of static HTML files, then you don't really need a framework.  But if your website will have lots of dynamic content that will get updated on regular basis, you should go with some framework.  That will make your life maintaining the website much more simpler.
Django is the most popular framework written in Python.  It has very good documentation and a strong community base too.
The site won't be that complicated and will resemble a modern blog (users, messages, news and other similar features).
Do I need to use a framework for this, and if so, which is best?
Pyramid, Django?