I tried em all and to be honest the only one that worked with every file i threw at it was Dice Player. The free version convinced me into 5 bucks and it was worth it.
Just google search Step by Step Guide on How to Play 720p, 1080p MKV on Android Phones/Tablets
You will find a simple solution to successfully play HD MKV in 720p or 1080p on all kinds of Android based smart phones and tablet computers