Nothing is best! It's all depends on the CODEC it used to store the video.
HDD cameras will save you the cost of SOME MINI DVs.
DVD cameras are alomost useless, since it stores in MPEG2, which compress between and within frames.
HDD cameras normally uses MPEG-4 codec, which is even bad. Editing is a headache.
Mini DV uses DV Codec, which compresses only within frames. Buy Mini DV cameras if you expect good quality from your camera.
Check this:
*www.dvdigest.net/Page.asp?NavID=135
*www.dvdigest.net/Page.asp?NavID=139