Microsoft's Bing for iPhone app was updated last evening with several new features such as Bing Interests, Bing News, a private searching mode, the Popular Now section on your Apple Watch and other enhancements.
I typically use Google's native search app on my iPhone, but Bing saw some rather interesting improvements in recent months. In my personal opinion, Microsoft's search-based app is better designed than Google's with richer descriptions and prettier images.
More importunely, Bing's popular searches feature produces way more relevant results than Google, at least for me.