We use Ansible because it's simple to write recipes (they are just YAML files) and simple to deploy (you just need a working SSH setup and you don't need a master server). We were reluctant to automate our devops with Chef and Puppet. Discovering Ansible was a relief.
We use chef currently but some of the new devops team have more experience with puppet, so looking for suggestions about how much success people are having with either (or others).