The two best choices are either DV-PAL (or DV-NTSC), at around 50% quality

Or

Photo-Jpeg at aorund 50-63% quality.

Photo-jpeg has a better color space, and is resolution independant, so you can do odd resolutions. If you don't need the extra color space, and are dealing with the standard resolution of DV, then DV is the better choice, as you an get a few more layers to play back at once.
All of this should be tested by you as well, as depending on your hardware configuration, you might be able to use better quality settings, etc. Sometimes though, I have found that the difference in quality might not be very noticeable (depending on what kind of screen you are using) compared to the difference in performance between different quality settings.

Personally, I almost always use Photo-jpeg.