I have done both . Niemeyer patterns have much better directions. DeJonge , if you get an old pattern they do not contain the papers. English is not DeJonges native language and she uses an interpreter for the directions in English. The DeJonge patterns directions have gotten better over the years , but the older patterns have not been adjusted or corrected.
Both have stunning patterns and are not for the faint of heart. Do look at the curves , deep curves are not easy to get perfect especially if its your first one of this type.
Last year DeJonge had a booth at the International Quilt show Chicago.... and her brother ( it think) was there , he explained they have worked through many of the issues we have had with her patterns. Her patterns now contain the papers , but older ones without are still in stores and in some online retailers. So before purchasing be absolutely sure it has the papers, as the patterns are not easily copied or transferred since they use a paper size available in Europe.