Engadget has posted an interesting post about the HTC Desire SLCD and AMOLED displays. While the AMOLED is more vibrant and bright, the S-LCD shows a sharper image (this is due to the AMOLED's PenTile pixel matrix that uses two subpixels per pixel instead of three). They also claim that the SLCD offers a better contrast - even though the AMOLED's blacks are much blacker. This is again due to the PenTile arrangement.
In the sunlight visibility test, the AMOLED actually comes on top, but both are hardly readable. HTC's glossy glass is to blame for this, really. In terms of power efficiency, Engadget say that the AMOLED comes on top - after 5 hours of showing movies, the LCD-Desire ran out of power while the AMOLED one had 30% power left (HTC and Samsung say otherwise, by the way). Here's a video comparing both phones:
A few weeks ago we posted a different comparison between the Desire's SLCD and AMOLED versions, which showed pretty much the same results - but the video has been pulled from YouTube since.