Bare-root are usually cheaper because shipping costs go way down minus the container and soil. Bare-root (dug up with all soil removed) are usually shipped as dormant plants or 1-2 year old dormant tree sapplings. Most mail order trees are bare-root. Container grown plants arrive as active growing plants at the right time for planting in your area.

Vera

I would add a note of caution to carefully check how the bare-root nursery obtains its bareroot plants. Some have been know to dig from the wild. Probably more common with woodland plants than prairie varieties, but worth checking none the less.

V.

Either bare-root or potted plants will work.

It's important to get the bare-root plants in the ground during the spring -- the sooner, the better. Alternately, they can be planted late in the fall. When they first come-up, bare-root plants usually require less watering than potted plants after the latter have been planted in the ground.

I have had good luck with bare-root plants but avoid the May sales of these plants. They need to be in the ground much earlier.