DV, QuickTime or iMovie
The DV format files are in a format designed in 1995, the compression of video has gotten, ahem, a bit better in the ensuing 20 years. That is why the file size looks so big. It is big.

.dv is a compressed format, but the audio remains uncompressed. What you need to do is go through the manual of the camcorder (usually available online) that shot the video (or something similar) and see what resolution it shot at.

Then you just convert the .dv file to an mp4 at the same bitrate and resolution and that will give you, probably, the best quality output. MPEG Streamclip and Handbrake should be able to do the conversion (if I recall correctly).

Or you can blow up the movie in Quicktime and choose the one that looks the best. It all depends on how much time you have to work on this.