1080p with no AA means it's probably very aliased. Sure its native resolution matches the TV, but the aliasing is still there and noticeable. Just playing a game at the same native resolution as your television doesn't make Aliasing go away. 720p w/ AA means the image may not be as sharp as 1080p, but there will not be aliasing. It will depend on what you care about: Sharpness (1080p no AA) or cleanliness (720p + AA).







