For creating AMIs? Probably Ansible or something similar. Chef is great for ongoing management of servers, but not so good for a one-shot config run like you would do if you're creating AMIs.
I still use it for that. Built a really nice packer based process that pulls in Chef cookbooks and applies them in zero mode. Even have an integration test of the resulting AMI in later stages using test kitchen (Chef's "killer app" imo) with the EC2 driver to spin up an instance with the AMI and run Inspec tests on it.
