Plugs are typically smaller, and younger trees. Cheaper by quite a bit as well. Bare root are bigger, have more roots, and take significantly more effort to plant, and also have a higher probability of having problems related to the planting process (bigger hole, harder to get roots oriented correctly, roots installed at an angle, etc).
With a decent planting tool, I can have a plug installed in under 20 seconds taking my sweet time. It's in a hole with no air pockets, no j-roots, and minimal compressed soil (only the volume displaced by the tool) - plus never having to get on my knees.
I did 100 bare root Douglas Firs. I'll never do another bare root conifer. You gain 2 years growth up front (time burned off at the nursery), but I don't think the tree is as healthy 2 years later vs what it would be if it'd been planted as a plug.