You can use Compressor and tweak settings to get a clean HDV 1080i50 to SD NTSC conversion. Prepare for long render times.
Alternately, consider (Using Compressor) converting HDV 1080i50 to PAL as ProRes. The convert the PAL ProRes to NTSC ProRes. You can even 'chain' the two in Compressor, though I prefer doing it in two stages. Takes less time than one HD-SD conversion with frame rate change.
Make the DVD from the NTSC ProRes movie.
If you don't mind a small (4%) speed change, convert the HDV 1080i50 to PAL ProRes. Then conform that to 23.98fps in CinemaTools, and use that 23.98 fps movie to convert to NTSC ProRes. There will be less motion artifacts that way.
Overall, the quality is in the settings. You also need to consider aspect - whether you want to see HDV's 16:9 as 4:3 letterbox or 16:9 anamorphic in the final DVD.
FCP Editor, Edit systems consultant