Definitely my phone. It can do what all my other I devices can do and is portable. All of the work I do on my Mac can be saved to my iPhone because of the iCloud which is always with me. The same for my Apple TV and iPad.
iPhone 5 is my current iPhone and also my favorite. I have owned iPhone 4, 4S, and 5, iPad Original, 4, and now Mini, Apple TV, MacBook Pro 2009, iPod Nano version 3 and then version 5.
I only have an iPhone and an iPad, but the iPhone is certainly my favorite. Even when I'm trying out other devices I still keep the iPhone with me. It is just easy to use and get what I need when I need it.
I have four iDevices, 2 iphone 5s', an Air and rMini. I can't say I have a favorite but that I really enjoy them all. They all work so smooth and have such good quality that I'm totally satisfied with the investment. Yesterday I fired up my old LG G Pad 8.3 and it really made me realize why I prefer my iDevices.