There's a variety of reasons I chose Ghost as my blogging platform of choice, but I'll focus on the few pros that distinguished the platforms I considered.
Publishers First
Ghost has made its mission to prioritize publishing. This means removing the resistance for organizing, creating, and publishing new posts. Though platforms like WordPress do a lot of that heavy-lifting, Ghost wins out by allowing publishers to have complete ownership of the publshing process from back to front.
As a completely stand-alone application, Ghost allows developers to completely own the process with an independent backend that one can run remotely or live online on the web. Few platforms offer that independence without growing to become too bloated.
Lightweight
On that note, Ghost was written to be fast, streamlined web application. Based on blazing-fast javascript, Ghost runs on node.js rather than php, the traditional scripting language that most blogging platforms use. Rather than trying to absorb the featuers of a full-fledged content management system, Ghost was designed to be dedicated to just publishing which removes a lot of the unnecessary dead weight.
Though nothing will probably beat out the minimalistic dropplets, an impressive flat-file, no-database, blogging system. Ghost seems to offer the right amount of weight in customization and ease-of-use that gives it enough muscle to be a true lightweight.
Readability
Few platforms have been as impressive as the clean, sleek layout that svbtle and medium have, but the themes to choose from the official ghost marketplace have grown substantially in the past year that Ghost has been out. Started by the Deputy of WordPress's Head of UI himself, Ghost was seeded and founded on good design. Over time, it's attracted more and more skilled designers to build some impressive replicas of medium and svbtle themselves.