VLC is always my first choice since I switched to MAC. VLC is good enough most of the time; however, It performs very poorly when playing my old RMVB videos, and it cannot display external subtitle file properly.
MPlayer OSX Extended is superb in this territory. Work like a charm!
PS: MPlayer OSX Extended is not the one in App Store. http://www.mplayerosx.ch/
Updated: I have switched to MPlayer OSX in the App Store. Extended stopped working suddenly and issues remains even after i restarted. So far, MPlayer OSX is quite ok. But when playing some full HD movies, VLC seems to have better preformance.