GadgetLove has a beautifully animated GIF of the iPhone. Watch as it transforms the first generation into the 3G, the 3GS, and all the others up through the present iPhone 6. A few models are skipped, most noticeably absent is the 5c, but I think its understandable which made it into the animation and which did not.
The body style of the iPhones 6 has as much in common with the original and 3G models as it does the 4 and 5 models. As much as I like all of the body styles, the look of the 1st generation and the Space Gray 5s appeal to me most. And yet, I would enjoy the 6 a great deal more if it were not for the antenna bands on the back. Personally, I think they look tacky, like the yellow highlight tape on the back of a school bus. ∞