The answer is not obvious. According to [1], mailing a DVD and streaming a film use about the same amount of energy. This doesn't include the energy cost of manufacturing the DVD, but stamping out plastic disks is cheap, so it can't be too high. On the other hand, other studies show that DVD players, being older, tend to use more energy than streaming boxes. For repeated watching, ripping a DVD and streaming it locally seems likely to be better.
Or best of all, stream the movie and store it locally for future viewings. But that's not allowed. DRM is killing the planet.
[1]: https://www.universityofcalifornia.edu/news/energy-cost-stre...