Edit: The thing I really like about Ansible is how unsexy it is, it's just a nice sane way of doing largely what you could do yourself with ssh and bash but in a language that doesn't make you want to cry.
I've been around linux since the 90's and Ansible feels comfortable, predictable and stable - what you would want in a piece of software that can be mission critical in the most fundamental sense.
Ansible automates even provisioning in AWS. I never really liked CloudFormation's way of creating stacks, so I began to use Ansible to document the application's stack, have used it to deploy systems running in EC2 with RDS, ElastiCache, SQS, SNS, DynamoDB, etc.
After provisioning/configuring I'd end up with an instance in EC2 with Docker installed and from there our CI/CD would just trigger the deployment playbook that simply would do a `docker pull` of the version tagged for release and start the container.
Ansible helped to also install our Splunk forwarders as running it from Docker was a hassle still not so long ago, so we would have the best of both worlds: configurability of the host machine completely with Ansible and packaging and predictability of deployment through Docker.
I advocate this stack as simple enough to learn and use with widely used tools without their fancy (and often broken) features. Even though they can be still a bit immature, they are production-ready enough.
Salt, like Ansible, is a response to the Puppet/Chef hegemony -- ruby and DSL's and tacked-together bits that are a nightmare to install and upgrade in themselves).
I'd suggest Salt did some things much cleaner than Ansible, and while it can be an orchestrator, and deployment system, it also excels as a configuration management system ... but I think typically people are talking about configuration management systems that are tightly coupled with more formal change management systems (of which I've found pretty much none that work well).
I'm even using ansible for ad-hoc stuff (tweaking a config, restarting a service) because it's easier to do that from a management server than log in to some remote host, get oriented as to the OS distribution and version, and run commends in the shell there.