The iPhone 4S is definitely the best phone I've ever used and this comes from a history of using the iPhone 3G, Nexus One, 3GS and most recently the Nexus S.

I have to admit, the main features that converted me were firstly the notifications system and second, the browser.

While it feels as if iOS had blatantly copied the Android notification system which I suspected before using the OS, upon actual usage it's quite different. Rather than having app managed notifications, I can now control my notification style from the OS settings menu. No more searching for an SMS app which gives me a popup or no popup option. No more fiddling around with apps to tweak their notifications the way I want them.

The browser is also extremely smooth on the 4S, particularly compared to the Nexus S and 3GS. Hardware acceleration definitely helps here and even rendering Google sites such as Gmail and Reader seem better.