VLC is indeed a good MKV Player for Mac, it can almost play all video, however, if you want to sync your videos to other Apple products such as iPhone, Apple TV, iPad mini, you need to convert them to some proper formats, what i use is the Video Converter, it can convert all videos to Mac and other Apple products comptible formats.
I use either VLC or MPlayerX, both free.
VLC will play almost anything you through at it, so it's handy to have it around, but MPlayerX has a nicer interface, so it's usually my first choice.
You can download them here:
- VLC: http://get.videolan.org/vlc/2.2.1/macosx/vlc-2.2.1.dmg
- MPlayerX: http://mplayerx.org/download.html
PS: Be careful while installing MPlayerX. It started using an installer a few months ago and the installer might install adware if you don't disable it.