What was the best iPhone?
The title says it all.
Obviously they could only have certain capabilities due to the technology of the time they were made.
Mine would have to be the original. It was made of the best material ever used for the iPhones--aluminum. It's the durable material they've used. It doesn't have the shatter problems of the 4/4S and it's not as cheap as the 3G/3GS.