As far as design:
I actually hated the scratchable plastic on the iPhone 3g/s
The cracking of the case was the thing that sucked
The iPhone 2G aluminum backing was easy to scratch too and had a different color underneath when scraped by car keys. Even the back glass of the iPhone 4 was less durable than its front glass and attracted fingerprints just the same.As far as design:
1.iPhone 2g
2. iPhone 4
3. iPhone 3G/S
I actually hated the scratchable plastic on the iPhone 3g/s
As far as function, the 3GS on 3.0 seemed the most fluid and smooth, but the iPhone 4+iOS 4 is certainly nice.
3G/3GS's design. 4's innards.