"Colors on the AMOLED screen are more vibrant and it seems brightness is a bit higher than the one of its S-LCD counterpart, which however has a more accurate color representation. The black levels seem pretty much equal, at least judging by the photos.
HTC Desire with S LCD screen meets one with AMOLED, they go head to HTC Desire with S LCD screen meets one with AMOLED, they go head to head
S-LCD on the left, AMOLED on the right • S-LCD on bottom, AMOLED on top
Still, the S-LCD screen on the HTC Desire has a slight edge in sunlight legibility. It also offers some improved power usage in the general case (though AMOLED gains an advantage if displaying mostly black images). LCD screens consume less power when displaying all-white content. "
You can check the reviews, http://www.gsmarena.com/htc_desire-review-468.php
"The Desire shares with the Nexus One a 3.7” capacitive AMOLED touchscreen of WVGA resolution. It looks marvelous indoors but if you go outside you won’t help but notice that sunlight legibility could’ve been better. It is the highly reflective surface and weaker backlighting that make it a bad choice for outdoor use."
Check the last 2 pictures.
"Outdoors, however, the N900 is an obvious winner - just look at the direct sunlight example down below. The AMOLED display on the Incredible is more difficult to read in indirect sunlight, and very challenging to look at in direct sunlight."
The main problem of AMOLED screens,is that they aren't as good as LCDs in direct sunlight, that's one of the reasons that Samsung uses Super-AMOLED displays on some of its handsets which work fine in direct sun-light and consume less power.