I dont use either. I prefer VLC or media player classic. either one of these 2 plays all my movies/tv shows with no hassle.
As for picture quality no 'player' will be better than another as it all has to do with the original file. If it hasnt been uploaded at a good enough quality no matter what program you use it will look the same. Granted you can probably tweak some settings but it wont improve the picture that much.