Whether 1080i (the native format of HD content on Sky and terrestrial) is a better output option all depends on whether the box or your TV is better at the process of de-interlacing to produce the 1080p full frame which is needed for the physical display. Try each for a few days to see what you think and bear in mind TV shows and movies can give different results because of their differing original framerates. Movies (and TV dramas that were shot like film) get each of their frames split into two sets of odd and even lines for 1080i transmission so they can be fully recreated whereas broadcast TV stuff is shot at twice the framerate so has to have half of its lines thrown away (or more commonly they were never captured in the first place by the camera) and "guessed" by the device converting it to 1080p. If this is done badly you can end up with weird thin line artefacts on the edges of high contrast moving objects. Particularly noticeable on scrolling news tickers.
