The only true 1080p is bluray.
Part will depends on the type of tv you have, does it always display 'native' and then what the native is for that tv, 480i, 720p, 1080i, 1080p. A CRT will be all ways be 'i', LCDs it depend on the model, plasma will be 'p', RPtv very. Most new tv's can 'upscale' a 1080i to 1080p native (if it is a 1080p tv). This sometimes can add noise to the picture. Mostly the tv is doing more work then if you had a true 1080p synal go to the tv. Some tv's are better then others at the prossesing, some tv's if you send a 720p to a 1080p 'native' it will look better then if you sent 1080i to the same tv, this is common when gaming.

So mostly depends on your tv model number.