<3 DuckDuckGo
I'd love to see Apple swap over to DDG when the contract with Google ends in 2015, and actually, I can easily see them doing that.
1 - DDG is one of the four options you're allowed to pick from in iOS 8 and Yosemite, so Apple is obviously aware of its existance.
2 - DDG is the only search engine that doesn't track you. What with Tim Cook's "They can cart us out in a box" or whatever, I think Apple could swap over to DDG, just to show how committed they are to user privacy.
And if users are free to swap over to using the other search engines, why not?
Plus, besides DDG's main claim to fame of not tracking you, I actually think it's the best search engine on account of !bangs and having the cleanest UI. The only time it ever falls short is when I'm doing image searches... I feel like Google Images normally returns exactly what I'm looking for whereas DDG's images are hit-or-miss.