Spike,
In Oz we have three applicable types of ratings (excluding GAAP). TWR (radar); Approach (radar); TWR/APP (procedural). The TWR (R) is for busy locations, with a separate approach unit associated to it; or regional locations class D aerodromes with airspace out to 30NM so they provide Approach and TWR services. So the answer to your question is; there is no preference, in our neck of the woods.