Essentially a container shares the kernel of the host, so uses less resources to run.

VMs are useful when you need more isolation or a different kernel (or need to add kernel modules).

For most purposes containers are the easy option.

I guess I could have a Container with a bind mount to a dataset that I want to be able to share over NFS or SMB, and handle that from whatever OS I put in the Container, right?

Yep!

But, I could also have a VM do that, and though it wouldn’t be able to share the data with other VMs, it can do it over NFS, can’t it?

Also yes, just a more complex setup with more performance penalty due to using NFS to share data into the VM.