MPC plays in very few apps and devices. FLAC keeps full quality at about half the size of WAV. An MPC file usually holds Musepack (MPC). MPC is at home in high-bitrate music collections on desktop players; FLAC is the usual choice for archiving music at full quality. FLAC cannot bring back detail that MPC compression already removed; it simply stores the result without further loss, in a larger file.
The defaults suit most files. Under Options you can trim the start and end.
This pair uses the compatibility engine, ffmpeg built for the browser, because MPC is not handled by the browser's built-in codecs. It is a one-off download of about 10 MB that the browser keeps, it is slower than the built-in codecs, and it takes files up to 1 GB.