I have the iPhone 3GS. It was the first iPhone given to me. I like it, but I like my iPhone 5, the first iPhone I ever bought much, much more. As lucastatic says…"It's a joy to hold, and the aesthetics constantly draw my eye."
I feel the same way. I love how my 5 feels in my hands. The 3GS, not so much. I never had the original iPhone or the second one and while I think they are attractive I have about as much like for them as I do for my 3GS. As to the iPhone 4 and 4S, personally I find them to be short, fat and ugly. That's just my opinion, lots of other people like the iPhone 4 and 4S and as it's an iPhone it's still a great phone. It's just that it's aesthetics (ESPECIALLY when you add in a bumper or a case) do not appeal to me at all.
But hey…you asked. 🙂