I prefer Media Player Classic over VLC because MPC can hide various parts of its interface at the press of a single button, it's able to easily hide any letterboxing (ie. black bars), and the player borders can snap to the video frame edges if you want. If you have any codec issues, just download the Combined Community Codec Pack.

VLC's only benefits over MPC, for my use, are that it has the necessary codecs already self-contained, so it makes for a very good /portable/ player; and its codec output info page, for such as finding the aspect ratio or bitrate, is easier to find and is laid out better.