Thanks to it's popularity, Jekyll has a large and active community of users. This means there is plenty of learning material available for Jekyll and it's easy to find help from other users when needed.
Middleman is a big piece of software, it's not simply a static blog generator. Because of all the functionality and flexibility it offers it can be a little more complex than other static site generators and a little harder to learn all of its bells and whistles.
Octopress is designed to remove all the time-consuming and frustrating tasks you usually have to deal with when using Jekyll. You don't have to write your own HTML templates or do any configuration to get started. The default template also takes care of any basic CSS/JS you need to write to get