Having had an AMOLED phone and an LCD phone, I think the iPhone 4's LCD display is a bit better. The AMOLED display apparently has an inherent colour balance issue that gives the screen either a pink tint or a yellow tint in low brightness. Never encountered such problems with LCDs, and not sure about Super AMOLEDs.

Only gripe I have with the iPhone's retina display is that it's so darned small...