madVR is a DirectShow video render that is compatible with many DirectShow players, such as MPC-HC, MPC-BE, Zoom Player, etc. It requires a decent GPU for best quality and has lots of options.
As stax76 alluded to, the differences are reasonably subtle. As long as it is working properly all video decoders deliver the same image, the improvements come from better methods to scale the image to the screen and convert the 4:2:0 video data to RGB for display.
Audio is similar, if you do not need to resample or mix the audio every method will give very similar quality. Video is more work because 4:2:0 is not directly usable so you have to do some conversions.
This post will probably take some Googling to make sense.
