[ZenoArrow]

This is an interesting one, in that most data on DVDs is already stored in lossy formats (such as MPEG-2 for video https://en.m.wikipedia.org/wiki/DVD-Video ). The best form of preservation is to rip the contents as a DVD ISO, which will use the same video and audio formats, as well as preserving extra features like the DVD menus. Any DVD ripper that can rip to a DVD ISO format and perform checksums on the ripped contents will suffice.

[eltoozero]

h.264 or h.265 is going to yield a much better compression ratio for equivalent quality, even after transcoding formats.

On the order of 2:1 or 3:1 vs MPEG2 format for DVD.

[ZenoArrow]

Lossy in top of lossy is never going to be the best approach for archival purposes, which is what the GP was looking for.

If the question was about balancing quality and file size I would've given a different answer.