Aaxis is right: you are asking on an Android forum, obviously most of us here choose Android over iPhone and we'll tell you to do the same. If you were to ask on an iPhone forum the answer you would get would be very different. I, for one, had an iPhone before my sgs2 and would never go back to it.
BUT the correct answer is "it depends what you want to do with the phone." As one example, a huge advantage of Android is how customizable and flexible it is. If you are willing to spend the time to learn all you can do with it to take advantage of this flexibility and customize it so it works for you, then I'd suggest an Android. If you don't want to spend the time and are willing (or even prefer) to use your phone straight out of the box, then perhaps you are better off with an iPhone. You should not rely on someone else's answer because it depends on how YOU will use the phone. I'd encourage you to do some googling on the differences between both platforms (TONS of articles on this out there) and decide for yourself.
Whatever you choose, enjoy your new phone!
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