When you tap on the URL bar in Safari and enter something to search for, your default search engine will find the results and show them to you. Do you know that you can change the default search engine used by Safari in iOS.
For now there a few big major engines (Google, Yahoo, Bing, Yandex and DuckDuckGo) can be changed by users. They are all good choices but default search engine decision is up to you. You can switch whatever you want it.
The choice you make here also impacts the web searches performed from Spotlight, as well as the selected text search tool. This choice has no impact with searching on page text function of Safari.
Update: Safari use Google as default Search Engine and Siri use Bing. While making a change to Safari doesn’t impact Siri but you can change Siri’s search engine by your command.