Twice I encountered breaking changes between versions that required manually upgrading minions. I also got the overall feeling Salt was built by developers, Ansible by sysadmins - and I fit into the latter bucket.
Ansible (originally known as "Fedora Unified Network Controller" or "func") was made for solving the problems automating Fedora Infrastructure.
Puppet did not make Fedora Infrastructure administrators happy. So func was designed around solving their problems, and expanded its scope as people found it useful. Then it was renamed to Ansible, the developers left Red Hat to create AnsibleWorks, and the rest is history!