Limnos wrote:
Note that the disadvantage in using an intermediate step such as Handbrake is with each re-coding step there is quality loss.
Yes and no. While technically correct that there is "quality loss" it is usually imperceptible. Handbrake is quite capable of producing good quality conversions. There was a greater "loss" when the source video was originally coded & compressed to produce the DVD.
I have transcoded quite a few DVDs using the old MPEG Streamclip and Handbrake and it's really hard to discern any loss of quality going from the DVD video to an MP4 output file for editing.
Also, there really isn't a choice in the matter. AFAIK, iMovie cannot import & edit the VOB files that are on a DVD. The OP will need to convert the DVD videos to MP4 or MOV to use them in iMovie.