With the recent release of Chrome for iOS, it's been a huge hit, topping the free downloads section of the app store nearly instantly.
The problem with iOS though is that it doesn't let you set other apps as default, like Android does. The only way around this is to jailbreak your device. So to make your default browser Chrome, you will need a jailbroken device.
Head over to Cydia and download Browser Changer. It's free. Once downloaded, head to the "Settings" app and find "Browser Changer", then choose "Chrome".
That's all you need to do and will now make Chrome your default browser.