With respect to claims of privacy, to my knowledge none of these search engines have been independently audited.
Because Startpage is an aggregator search engine that relies on google.com, I have grown discontented with Startpage search results. Startpage search results have grown frustrating. More often than not the results contain a lot of noise and duplicate results. More often than not the search engine algorithms are designed to guess what I want rather than provide specifically what I requested. The shotgun approach.
While I had been alternating between duckduckgo and startpage, now I just use the former.