Ranked in these QuestionsQuestion Ranking
Pro Very lightweight, smaller attack surface
The OS is tiny and has a much smaller attack surface compared to other distributions.
Pro Automatic updates
Automatic updates means better security and reliability.
Pro Docker pre-installed
Docker comes out of the box.
Pro Great documentation
Has guides for installing systems like Kubernetes, setting up etcd, and using cloud-config to manage hosts.
Pro Built on systemd
Uses unit files for managing all services and journald for logging.
Con No package manager
CoreOS has only the minimum for being a host. It doesn't even have a package manager. Alternatively you can start a container with any software you need.