iPhone iPhone iPhone, why well one good reason, in June apple will be releasing software update 2, what does this mine I hear you ask, well other people will be able to write apps for the iPhone so it will have many more features to it. The only thing is, maybe or maybe not a new iPhone will be out in June, this means if you don't mind spending £270 on a phone then wait, or try and get an 8GB one now from O2 and only pay £169 but good luck with that as I don't think there are many left.
But if you want a phone with many features and expandability then the iPhone is the only phone out there that gives you everything you want.