Plasma screens tend to have much more reflective (glass) screens, whereas LCDs such as my Sony Bravia 40in have a less-reflective matt screen, which is one of the reasons I chose it - I too had no choice but to place it in the corner of the living room next to the main window, which means I get fewer reflections on the screen during daytime viewing than on a plasma.
Not the most scientific reason for choosing a TV, perhaps, but it works for me!