MKV is a very well established video container, it's not actually an encoding 'format' as such, it's just a container for various other formats of video and audio, H.264 video and MP3 audio for instance.
My LG TV, Sony Blu-ray and VLC play most MKV files fine from USB, If I run into problems it's usually because of the audio decoder (for instance my TV doesn't have a decoder for Dolby DTS).
Anyway, if you are playing them on a laptop then it's easy to get the right decoder. Install this:
http://www.codecguide.com/download_kl.htm