Preferably a nice solid raw blip, rather than a plot extracted electronic symbol; with plot extraction you can never be sure that all aircraft are showing, whereas with proper raw radar you can. Raw radar also makes it easier to identify non-transponders using the turn method, as you see the turn immediately, whereas the processor for a plot extractor often takes several seconds to realise a target is turning, and thus often displays a new heading in consecutive 'paints' rather than giving a track history showing a constant rate of turn.