Very interesting comments guys,
my Sony TV has a native resolution of 1280 x 720p and maybe that explains why I haven't see any difference though.
It does, however, accepts 1080i (when I upscale the resolution over the players. IOH, it doesn't accept 1080p at all).
According to what gmichael said, I might as well leave the resolution always at 720p though.
Thanks for clarifying that!