Use whichever one you're more comfortable with and that suits the rest of your stack best. There's nothing Jails are going to allow you to do that Linux containers can't do. All the shared-kernel workload isolation schemes are comparably safe.

For starters, Docker runs as a daemon.

For starters starters, Docker is a few layers up in the stack from jails. You would be better off comparing runc to jails or just cgroups+namespaces to jails.

No.

Docker and runc are very similar.

Docker run Docker containers. runc runs OCI containers.

And jails operate at a similar level, though without an image format.

Right, so jails do not have images or any of the tooling around building and distributing images which is the vast majority of what makes up docker. This is why cgroups+namespaces are much closer to jails than docker is.

There are systems which build upon jails such as iocage and ezjail which are more similar to docker.