After trying everything on Gizmos (from where I took the current list) I found myself with two options: MPC-HC and SMPlayer. These couple of players share the same qualities; low resources, good sharpness of image, ease of usage, stability... I finally decided on SMPlayer because the UI is more configurable. There's always VLC on the background for whatever can't be read by SMP (like ISO files). So, what's your default player?