While other web browsers exist and thrive on iOS, Safari is the one Apple includes with it’s iOS system software, and it’s probably the one most of us use often, no small thanks to the fact that it’s integrated at the system level. Every click through, unless third-party apps (like Mailbox) allow something different, takes us to Safari as our main browser.
Therefore, if you’re looking for ways to protect more of your privacy, you’ll want to enable the Do Not Track feature in mobile Safari, as well as possibly block cookies, which are bits of code that store your preferences on website servers for return visits.