Having used Posterous no for few weeks I am moving my posts to Blogger. Don't get me wrong I like Posterous I really, really, do! I like the ease of use, and how it can deal with about any content you throw at it.
What brought me to Blogger is its connection to Google. I feel it will integrate best with the web I use.
Posterous is great to create with many people to get a snapshot of an event or vacation. Sharing among several email addresses. It is also great for people who just was to create and not worry about being an admin.
At the moment Blogger does not support importing a Posterous blog. I only have a few post, so my plan is export my four post to this new blogger page one at a time. The post that follows this will be my first post from Posterous. I will then continue to use Posterous and enjoy it, but this page will be my main blog.