Engadget is the latest blog to test the iPhone's new "Retina" IPS-LCD display against Samsung's Super-AMOLED (Galaxy S phone). The iPhone display is much brighter, and actually has a slightly better viewing angle. When viewed outside, they actually prefer the Super-AMOLED, although the displays are quite similar in that area. Obviously the iPhone's 4 resolution is way better. The Super-AMOLED is said to have stronger color saturation and sharper definition, even though it looks pixelated compared to the iPhone's display. Basically what they say is that both displays are good, and it all comes down to personal preference.
Check out the full post, it includes a lot of photos and a couple of videos.