1. Plain and Simple - no bells and whistles
This is the easiest publishing tool I've come across. Easily add images, videos, instagram posts, etc to your content. Your content is even auto-saved while you write, so you never lose your post!
Ghost also has a Mac and Windows Desktop app.
2. It's Ridiculously Fast
Speed is the latest design feature for most modern sites. Ghost is built on the latest Node JS platform to allow pages to load in < 1 second.
3. You are in control of your content
I love platforms like Medium and use them for my own content, but I don't think a platform like this should be your primary platform where host your site. What if Medium starts charging a hosting fee?
With Ghost you can integrate into other platforms and automatically send content to Mailchimp, Medium, etc.
A few additional resources if you're interested in learning more.