SD: The default codecs are good. (DTS is pass-through only.)
HD (MKV, M2TS, TS etc.):
- H.264: MS decoder in RTM is good, but MPC Video Decoder is better.
- VC-1: MS decoder is good but does not support GPU hardware acceleration (not a big issue for a dual core processor through). MPC Video Decoder is better (but this does not support interalced VC-1). VC-1 Tweak + ArcSoft is a better alternative.
- MPEG-2: MS decoder is good. An alternative is CyberLink.
- HD audio: ffdshow Audio Decoder is the best. FLAC: madFlac.
BTW 7MC internal player uses the default MS codecs in MF pipeline for M2TS, TS (and more). So you need a tweak to use non-MS filters. Read:
- A Quick Guide to Playing M2TS in WMP12/7MC
- DirectShow Decoders Used in WMP12/7MC