An orbital sheet sander will be nice because it will fit into corners and will be easier to maneuver. However, it might be a little too rough and leave scratches.
A random-orbit sander is going to be more effective all around it will have a better finish with less vibration making scratches less of a possibility. If you won't need to do a lot of maneuver I'd say you should get this one.
This has been my experience anyway from working with a Minneapolis plastering company for so long.