I cant believe anyone can really ask this question. Come on, AT&T has the last word in phones-iPhone 3G.
It's not a matter of choice but its universal truth that iPhone is the best phone on the planet.
iPhone can be customized as per user needs. It has many application for every one.
I like general knowledge and quizzes so I have wikipedia,world wiki, US constitution, US manual, 100 words, Talking Dictionary and many more.
If you are more into songs and movies, you can install Pandora Radio,vSnax,ORB Live(TV),i.TV, Movies. And if you are into game then Asphalt 4 , Raging Thunder,Cube Runner,X-Planes and 1600 other games.
You can also install Fring and do voice chat on SKYPE with other SKYPE users.
Apart from these you also have many application for Business(Oracle Business) and Finances and quick references like around me(it tells you gas price,restaurant,other point of interests around your current position)
Apart from thousands of great feature one more thing iPhone has and that one thing makes it the best gadget that is the amazing execution of all the features. Every feature becomes a benefit for users coz of its stunningly spectacular maneuvering and navigation.