https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/hevc...
I'd be pretty surprised if there was a major difference between them. Maybe some bugs in the rendering path, or one player isn't doing threads properly?
Also what gcb0 said is true as well - but not everyone needs subtitles for their videos. My 'expertise' in media player selection is based on getting the absolute best quality playback for my anime.
My primary reasons for switching from VLC were not due to efficiency - but due to shadow being washed out and the NVidia color issues. Both "fixable" in that you can "improve them" but not quite "remove them entirely". (Both issues are easily Google-able as well)
There are many, many, many image comparisons between VLC and MPC-HC (and sometimes MPV for Linux). The one thing in common is that MPC and MPV both look very similar while VLC always has a washed out look and occasionally faulty colors (by default). Unfortunately, many people are terrible at screenshotting the exact same frame but even from similar frames one can pretty easily spot the differences between VLC and MPC-HC.
Example of the shadow/color differences:
Side-by-side w/ CPU usage difference: http://i.imgur.com/xJnrS2f.jpg
http://screenshotcomparison.com/comparison/176895 (excuse the distortion, I was 1px off on my cropping)
E:
Some people prefer the washed-out look finding it more aesthetically pleasing. That's fine and I'm cool with that, long as I don't need to watch anything with them. Many people also "don't give a shit" because they'd never know the difference without seeing the side-by-side or comparison of the frame. That's fine too - but not something I personally agree with. :) I prefer better quality even if I have to looking for it.
Your two culprits are that someone's YUV->RGB math forgot that Y needs to be expanded from 16-235 to 0-255 - possible but really surprising! - or that one player implements gamma correction and the other doesn't.
Gamma correction might look nice, but it can't be called correct unless you've profiled your monitor, set the brightness level, not changed your ambient lighting levels, and turned off all the nonsense LCD options like "contrast".
BTW, the only rendering bug I ever expect to see is the difference between Rec.601 and Rec.709 colorspace, which just kind of makes green colors look different. So this is pretty extreme!
That's typically my argument, but others simply "don't care" how the author intended, they want what looks better to them. Which is fine - as long as I'm not watching it with them. Because I actually do care how the author intended something to be seen.