The dwarf will probably produce fastest but will have the shortest life-span. Semi-dwarf is a decent compromise for the available space you have as it will allow closer spacing than full trees but without the need to prune as carefully to control final tree size. Full size trees generally take the longest to fruit but will last for generations.

I would recommend you identify compatible pollinators for your existing trees and make sure to plant at least one pollinator near your existing trees. Plums can often only be pollinated by others in their same "group", and apples sometimes have different bloom times (early, mid, late) so that an early bloomer may not be able to pollinate a late bloomer if their bloom times do not overlap.