When comparing MplayerX vs VLC, the Slant community recommends VLC for most people. In the question“What are the best video players for macOS?” VLC is ranked 3rd while MplayerX is ranked 6th. The most important reason people chose VLC is:
VLC is licensed under the CC-SA v3.0+ and available on Windows, OSX, and Linux with source code available [here](http://www.videolan.org/vlc/download-sources.html).
Specs
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Pros

Pro Pleasant Mac Style view
MplayerX fits in OSX environment perfectly with it’s hot keys and plain, but stylish design, giving pleasure to work with

Pro Players “memory” of a last reproduced file
If turned off, player will start file reproduction from exact spot it was interrupted on

Pro Smart-play or automatic next video file search
For example, if number of files with sequent names are mashed up and thrown in the playlist, MplayerX is able to reproduce them in right order

Pro Smart multi-touch control
Convenient track pad commands, that allows user to toggle full screen, change frame size, aspect ratio and volume. To learn more, watch an easy and understandable "how-to" youtube video in the sources.

Pro Compatibility with other Apple products
File reproduction can be controled with an Apple remote, that awards user with more freedom. Furthermore, dirrect pass through is possible. Start streaming, connect and enjoy your home theatre

Pro Softwere was designed specially for OS X
As OS X is the only supporting system, the amount of bugs and problems is minimized. This also means, that player can play .m4p, .mp4 & .mov video files.
Pro Free, open source, and cross-platform
VLC is licensed under the CC-SA v3.0+ and available on Windows, OSX, and Linux with source code available here.

Pro Simple to setup and use
VLC is an incredibly robust application but very simple on the surface. It makes playing music simple, yet still manages to give the user all the tools he/she wants in a music player.
Pro Very versatile and easy to use
Pro Doesn't require additional codecs
Everything VLC needs to play media files is contained within which means no outside codecs are needed. This makes it one of the most hassle-free music players as it can play virtually anything as soon as it's installed.
Pro Tons of advanced settings
Besides basic configurations, video player has an extensive amount of adjustable settings.
Pro Doesn't manage your music library for you
You organize your music into folders any way you want. Want to play an album? Drag and drop. No tags, no confusion, no fluff. Easy.
Pro Can be almost completely keyboard-driven
VLC includes keyboard shortcuts for most actions. The video player can be controlled with simple and customizable keyboard commands.
Pro Surprisingly Lightest on Resources
Yes. Lightest. Even better than the ones known to be light. Both when playing music, only a single song or when playing a video. Either in terms of Ram and Cpu. Compared with almost all, including the ones from Windows like mpc-hc .. or light ones from Linux like Alsa Player, Audacious, SmPlayer .
Pro Can play every format video available (as of 2017)
Pro Supports a GUI interface and an ncurses terminal interface
Pro Can easily stream music across your home network from any device on the network
Using sftp/ssh music (and videos) can be streamed from any server on the network to any device running VLC. VLC can also be used as a webcam for streaming and snapshots. Amazing all in one package
Pro Large amount of extensions
VLC has a large amount of extensions.
Cons

Con System crash is more frequent
MPlayerX creshes occur more often than in usual video players. They should be tackled properly.

Con High CPU usage is possible
Sometimes after the player or OS X update file reproduction can demand a significant part of CPU usage

Con No proper playlist feature
In spite of easy and comfy smart-play, in general playlist isn’t user friendly

Con No retina display support on old OSX
MPlayerX does not support retina display on OS X older than Mountain Lion, but amount of Mac’s with older OS X are quite rare nowadays

Con Not really meant to be a music player
VLC is made to be a video player. Therefore, it won't carry out actions such as managing your music library.
Con Lacks libraries and advanced music player features
VLC is a media player first and foremost. There is no library management (aside from playlists), limited usage of tags, and no rating system. VLC is best at playing a file directly from a folder, but falls behind when it comes to helping you manage or find good songs in your music library.
Con Absence of personalization
VLC Player has only one basic interface in white or black, and overall personalization opportunities are quite narrow. Unfortunately, you're pretty much stuck to the default look.
Con Contains some insignificant but irritating flaws
Despite all keyboard shortcuts, the width of the picture can't be controlled by trackpad. Besides that, the VLC start-up window doesn’t open at the same place or the same width at which it was previously closed.
