Sure, my 4S is beautiful, but it just doesn't feel right in my hand. Something about the aluminum/glass seam bothers me, and so I got a slim case and never looked back.
It's like those tiny micro-sized dogs.
It does have quite hard edges though, and I've wondered if they would get annoying after a while.
I never felt particularly either way about the 3GS hardware - it's ok, but nothing special in my opinion.
I will say that I'm the only one I know who considers the iPhone 4 to be a complete abortion of industrial design. It's fragile, it's unpleasant to hold due to sharp edges everywhere, and I almost always have to spin it around in my hands like a trained seal every time I pull it out of my pocket, because (unlike the 3GS) it's difficult to tell how it's oriented by feel alone. None of these things are true of a good design.
Apparently you can pull the SIM out of an AT&T iPhone 4 and wedge it directly into an unlocked Galaxy Nexus HSPA+, even though the iPhone takes a micro SIM. I ordered one of the latter after the iPhone 5 (non)announcement yesterday and am looking forward to seeing how that hack works.