However, once you start querying very specific things, it tends to fall apart. Just today I wanted to see if the a particular company utilizes any Machine Learning and searched for company-name machine learning. No top hit contained all three keywords or anything related to AI. On Google the top hit was a company research institute and contained all 3 keywords.
https://duckduckgo.com/?q=tiger
Recommendations: animals, military, people, movies, bands, organizations, technology, ... with a pretty picture, a subtitle, and a short description.
Top results: Wikipedia, Tiger Direct (a shop), WWF, Defenders of Wildlife, Tiger Woods, Detroit Tigers (baseball), ... (infinite list.)
https://encrypted.google.com/search?hl=en&q=tiger
Single recommendation: Tiger (Animal), with a pretty picture, the life expectancy and the scientific name.
Top results: Tiger Airways, Wikipedia, Tiger Stores (a shop), WWF, Tiger Direct (another shop), Defender of Wildlife, ...
Special results "in the News": Tiger Airways, Tiger Woods.
I've been happily using DDG for almost a year now, but I still use `!g` regularly because it does get confused sometimes (point is: no search engine is perfect, but DDG makes it easy to redirect your search elsewhere.) I switched because google was pushing g+ too hard, experimenting with the presentation, customizing the result list based on my profile, and it was breaking my flow (like the popup "make google your default search engine", I get why they do it, but it required unwanted attention.) Somehow DDG convinced me that they would be less invasive.
But it does have a much nicer UI, and there are lots of searches that it does about as well as Google. For programming stuff, the !bang searches are nice (https://duckduckgo.com/bang.html) -- I can type "!mdn createElement" or "!php obscure_function" and get straight to the official docs.
For broader topics, DDG's Wikipedia preview is a nice feature, the row of embedded images across the top for famous people is handy, and for everything else, I find the search results to be more readable than Google's.
Well, they are in your browsing history, and Google knows it?
So unless Google have started to do browser fingerprinting, which I don't think they have, that shouldn't be the answer. At some level I believe that Google is just better at understanding my request, regardless of how poorly I formulated it, while DuckDuckGo just returns pages where some of the word match. Given that I don't know how any of the two search engines work I may be completely of.
Google clearly uses these logs to "customize" your search results, even when you check the placebo button to "disable" your history in the google account options.
Not having an account (or deleting local history) doesn't matter much, as they reconstruct a PK from all the entropy your browser leaks. (see their recent "we already ID your browser" reCAPTCHA update that no longer shows a scrambled image)
Harder to tell for Google Search - unlike YouTube I never see any indication that search results are based on my history, so any manipulation that's happening is opaque (I never search while logged in, so I don't know if the behavior is different in that case)
As DuckDuckGo has become better, it also seems that Google is becoming increasingly worse, at least with general searches.
Interestingly enough where Google shines is finding pages that I sort of know exists. Queries where "I know I saw this on Stack Overflow" or "I've seen this exact text somewhere" and localized searches (Although DuckDuckGo have become a lot better recently).