Android certainly

Why coz
A. You can choose from a wide range of phones
B. You don't usually have pay for apps.
C. If you get bored of it you can install a new ROM and now I think you can also install Linux on phone.
D. It is hugely customizable

Q: Do you think people buy iPhone coz of the ads, example tag line "if you don't have an iphone you don't have an iphone"

My first mobile was Nokia 1100 =D brother of 3310