Only VLC media player is my favourite. I use only this player because it support most files so i don't need to use any other media players.
BS Player because I have had no problems to open basically any video. When you install it it automatically installs all the codecs needed. Also I like it because I often watch non-english speaking movies and once you start the movie BS Players instantly searches for adequate subtitles for the movie and asks you if you want to download them. You just click download and voila - you have found good subtitles for your movie in a matter of 1 click na 3 seconds