MPC right now. I tried powerdvd and windvd 7 and both sucked major balls. Bloat and nothing else plus sound in powerdvd stopped working after a while and in windvd the black bard up and below video when watchind anamorphic widescreen would actually be gray, not black, drove me nuts. So right now I'm using MPC, my second choice would probably be powerdvd 4.