Engadget has posted an interesting comparison between 6 different Android phones: MyTouch 3G, HTC Hero, Motorola Milestone / Droid, Acer Liquid, Google Nexus One, and Samsung Galaxy (laid out clockwise in the image below). Two of these have OLED displays, the Samsung Galaxy and the Nexus One. Engadget say that the best one is the Nexus One's 3.7" AMOLED. You can see for yourself in the following photo and video:

Android phones displays photo

Kyulux - Hyperfluoresence OLED emittersKyulux - Hyperfluoresence OLED emitters