I have VLC installed on my Mac but I only use it if I'm going to watch more than one episode at a time. If I'm just going to watch a single episode I usually use Quicktime Player with x264 core audio codec. I've found Quicktime's "Cache" option really useful for playing .mkv files. In VLC the mkv's would often drop frames or stop playing video entirely, the cache (video, audio, text or all) option in Quicktime eliminates this problem. Media player classic still hasn't come out with a stable Mac version so for the time being, I'll stick with Quicktime.