When it comes to server provisioning, I've only had experience with
Chef. The new place I work in uses ansible and I was tasked with
writing a playbook for deploying and configuring some of our software
there. The whole experience was overall good. My main gripe with
ansible is that it uses yaml files for running actions.
I think that's a huge drawback: instead of having the full python language at your disposal for writing playbooks, you're limited a weird yaml file format that gets in your way the moment you want something more complex. On the other hand, I haven't read enough ansible to come across someone complaining about this decision, so maybe the people using it don't see this as a problem. Also, python, unlike ruby is not a good fit at all for DSL languages. So I imagine that the creators had no choice but to use a configuration file format like yaml instead.
One thing ansible gets right is ansible-galaxy. In Chef, if you want
to use a cookbook, it has to be cloned in your Chef repository. This can
lead to the temptation of editing the cookbook directly, as outlined
here:
https://github.com/dfdeshom/thoughts/blob/master/2016-06-10-chef-anti-patterns.md
and is somewhat of an anti-pattern. In ansible, you don't have to
worry about being tempted, you can install external roles in a
separate folder ansible-galaxy install --roles-path roles/galaxy -r external_roles.yml on-demand. Ansible being agentless also helps
here, because only the deployment machine has to worry about having
the right roles.
The other thing it gets right is ansible-lint, which
is great for people like me using
ansible for the first time, as it forces you to write clearer
playbooks and stick to conventions.
For now, I still think Chef is the superior choice: you can't beat the ruby DSL and I don't trust agentless monitoring tools as much when it comes to making sure your servers are configured the way you want them to at all times.