mp3 is probably the most common lossy audio format, flac the most common lossless audio format.
Generally it is recommended (out of the history) to use a Sample Rate of 44.100 kHz for audio files and 48.000 kHz for video files. You won’t hear a difference between those 2 if you’re older than 20 years – but I would definitely recommend to stick with the sample rate of the original file as conversions always bring a (even though small) loss in quality.
These are my recommendations
AC3 Audio (lossy, Dolby)
2.0 channel AC3, recommended bitrate 256 kbps, recommended sample rate 44.100 kHz
5.1 channel AC3, recommended bitrate 448 kbps, recommended sample rate 44.100 kHz
MP3 Audio (lossy, 2.0 channel only)
recommended bitrate 256 kbps, recommended sample rate 44.100 kHz
Lossless Audio (FLAC)
FLAC 24-bit files are usually available in 96kHz and 192kHz versions, though a few albums come in 24-bit/44.1kHz or 24-bit/48kHz. The 24-bit/192kHz versions are the highest quality files commonly available, and are identical to the studio master.
Therefore the recommendation is to get 24bit flacs in 192 kHz.