I do not know about Ecosia, but DDG does not use only Bing. According to Wikipedia, it uses over 400 different sources. So in theory, given they have a smart enough algorithm, DDG should be able to produce better results than Bing.
Pretty sure the search results are from Bing, while those other 399 sources are for other things, like quick answers, dictionaries, translations, currency conversion, flight search, etc.
