I found geneanet very good especially for French relatives. The origins of our family is both German and French. I found detailed info on my father's uncle, who emigrated from Frankfurt to Paris in 1900 and later fought for the French against the Germans in WWI. His brother was fighing on the German side. Via Geneanet I found his military records and another Family tree that included him.
So to answer your question GENEANET is very useful as an addition to both MyHeritage and Ancestory.com. It is also a lot cheaper and has some nice functionality which you don't find in MyHeritage and Ancestory..