The first iPhone and the iPhone 4 were the best designs in my opinion.
As for the 5 and 5S, pictures never did justice to them. It was when I saw the 5 physically that it felt like the elegant Apple hardware I love so much.
The 5c actually looks great too, like a throwback to the 3G and 3GS.
No matter what the new phone looks like, it is something I'll be wanting the moment it is announced and I'll be getting the moment I can get my hands on it!