Following the native resolution of DVD standards, from my point of view, the optimal encoding setting for dvd would be the following.

Note that we always upscale one of the length of the movie instead of chopping the other one as many would do. this ensure keeping all the detail contained in a given dvd frame, as long as the final encoding bitrate allows for these details to follow.

PAL 720×576 25 fps

NTSC 720×480 29,97 deinterlace to 23.976

Widescreen PAL 1042×576 1.77

Fullscreen PAL 768×576  1.333

Widescreen NTSC   854×480  1.779

Fullscreen NTSC  720×540 1.333