Off the bat I'll say I never had the best results with the default setting presets, especially the "fast" ones.

If this is a casual project, just try another default preset first.

Try any of these. Keep in mind it can make your machine (especially a laptop) work at 100% CPU for a while. The higher the quality the longer it will take. You can run one of these and if it's satisfactory, then all is well.

Of course, if you want to optimize for quality and filesize, without ripping the same DVD multiple times, one option is to crop a 1-2minute clip out of the video to test on, and try processing it using different settings to compare before running it on the full DVD.

These are still sort of "one-size-fits-enough" kind of presets. If you want optimal results, it depends on your use case and expectations, how many DVDs you gotta go through and whether they're all somewhat of a similar format.

If you want to tweak further... stay tuned because I started writing way too much text for a reply like this so I'll likely make a quick guide its own post soon :P