Well, Ive never had the chance to use DVDx, but from what Ive heard its really easy to use and its not too hard to get decent quality rips.
Gordian Knot may be a little tough to use but after a while it gets easier. Gordian Knot probably has more options for you to play around with compared to DVDx which enables you to tweak your encode to increase quality.
GKnot has the compression test which is essential if you want to have filesizes close or exactly to the one you specified.
GordianKnot uses Avisynth to frameserve your d2v project into virtualdubmod which allows the encoder to encode the vobs in their native colorspace of YV12. Im not sure if DVDx can do that.
Since GKNOT uses avisynth to framserve your d2v file you have your pick of probably over a hundred filters that you can use to improve the overall picture of your movie.
Also not all dvds were made using the highest standards; some of them might be so bad that your only recourse is to use a filter or combination of filters to correct the problem. Im pretty sure DVDx won't be much use if you get your hands on a badly transferred dvd.
Well Gordian Knot makes movies of better quality if you know how to use it. If you make a mistake then the result may be really bad.
In the other hand DVDx is very easy and gives good results.
You can try them both. Find a GordianKnot guide at this site and see the results. If you find that they are the same or worse that DVDx there is not need to use Gordian Knot. If you find the way to achieve better quality, then congratulations!
GordianKnot uses Avisynth to frameserve your d2v project into virtualdubmod which allows the encoder to encode the vobs in their native colorspace of YV12. Im not sure if DVDx can do that. I think you can... although all those funky letter combinations confuse me ;P
