Its hard to believe, because tracking and especially tracking over search history both over the immediate term and the somewhat longer term is exactly what enables Google to surface such good results.
I've disabled search history and Google still tends to give me the most relevant results. Perhaps they also do some customization based on session cookie or something (I know YouTube does for recommendations) and I'm pretty sure IP location still plays a role. But I think it's mainly that I know how to ask Google for what I want, not that Google knows what I want necessarily. I still give DDG and Bing a chance once in a while, just in case, but old habits die hard.
I understand the theory behind all that but I'm preferring the results DDG is now giving me. The bangs feature is also really nice.
I actually used DuckDuckGo about a year ago but I went back to Google after a month as the results felt crap, but I gave it a try recently and haven't looked back.
DuckDuckGo's results have definitely improved over the last year. I now prefer DuckDuckGo's SERP UI over Google's and really like the !bang searches. I only need to use Google (!g) when looking for some very technical or recently-crawled pages.
