I'm a little bit surprised to see StackStorm directly compared to Ansible and SaltStack. There's certainly overlap in capabilities, but in my mental model of the space Ansible and Salt are primarily configuration management, while StackStorm focuses on event-based orchestration.

In my environment we're using both Salt and StackStorm very effectively. Salt for CM and StackStorm as a platform for building automated, event-driven tools. They're really very complementary, especially since both are Python-based.