I cant explain why dvd-decrypter some times does not work - apart from a few specific versions that had some known bugs that got fixed quickly by the author - but it is my experience from a long long time of using both, that the failurerate for dvd-decrypter are larger than that of smartripper. By failurerate I only mean when creating a backup that dvd2one does not "like"
Using smartripper I have only had 1 single troublesome disk that it could simply not decrypt. Using dvd-decrypter Ive had several disc's that seemed to be ripped allright but did not work well as source for dvd2one. Reripping these using smartripper instead has allways cured the problem.
Dont misunderstand me, Im not trying to badmouth dvddecrypter in any way - I like dvddecrypter - I think the author has made a great ripper, and it does have alot more options than smartripper - but as with all things, sometimes the simplest just works best for certain things. My primary ripper is dvddecrypter in most aspects, but for certain things like creating a source for dvd2one I allways use smartripper - theres no doubt in my mind from countless tests, that this creates the best source for dvd2one. And its easy - 2 click and your done.
Therefore as workflow that never goes wrong, its very simple.
Rip full backup to harddrive using smartripper - do not try to change anything (remove titles, audio etc. with the ripper), dvd2one likes an untouched source, use dvd2one to select audio etc. instead. Then let dvd2one do its stuff and finally burn the dvd-folder using your favorite burningtool (doesnt matter which one - noone as better than the other - if you know which settings to use)
Using this method I've never ever had a single failure with dvd2one - if you search the forum you will find plenty of posts with people that had problems with certain dvd's - the common thing about these has allways been the use of dvd-decrypter or people not ripping a full backup to use as source.
just my 2 cents