... and another part of the answer is what you'll be targeting for output. To preserve the original quality, you'd want to output to DVD in MPEG-2 (which is what the VOB contains)... that would mean no transcoding that might result in loss of quality.

That said, I've transcoded things for various reasons and have trouble seeing a real difference... of course, everyone's perception is different.

If you want to respond with your output target, I'm sure folks here can offer advice on what specifically to do so you don't have to use trial and error...