Nick,
I'm a Sky man rather than a Freeview bloke so perhaps not qualified to answer you. But..both deliver the same sort of input..give or take. The right scaler (bias admitted here, I am a Lumagen dealer) gives a substantial improvement to the PQ.
HD is coming but no sign yet of it on terrestrial - Sky only at the moment and at what cost?? I have Euro 1080 (aka HD-1) here and it is sensational sometimes, depending on source material, some is brilliant, some less so. The programming is dire - treat it as a demo channel and it is great, but not a channel to watch for your evening entertainment.
A scaler is your answer, much improved PQ with existing sources and wait until the HD "revolution" turns into reality.