Good point. I think a lot of our answers were based strictly on looks. I definitely agree that the 3GS has a more comfortable 'feel' to it. I notice it every time I pick up my old 3GS. Then I see the screen and I'm blown away by how pixelated and blurry it looks and the fact that I used to think it looked good. So, the iPhone 4 is superior in many ways, including looks, but the 3G/3GS is more comfortable to hold.
Although I love my iPhone 4 best, I did like the tapered body of the 3gs.. I could easily grasp it from the table and pick it up and had a firm grip and I have to use a little more caution with the 4.. that's the only design feature I liked better on the 3gs.
I never had the original iPhone so IDK what that was like. I had the 3G and the 3GS and I was soo used to them. I didn't like the plastic back or the thick chrome bezel but my Incase Sliders covered that up.
I thought I would HATE the design of the iPhone 4, but I grew to like it, now I LOVE it and it is my favorite. I can do more with it (cases look awesome and bezel/antenna color covers make the phone look even better).
Also, this design looks so sophisticated and sleek. Hands down, IMO it is the best design by far.