Depending on the lighting in your room, If its really bright with alot of windows and light coming in, then maybe Plasma might not be the way to go..
LCD to me isn't the greatest, My friend bought a good quality LCD tv and on HD material, its fantastic, but with Standard Def. from his cable company its looks dreadful. In stores you should make sure you get to see what the SD material looks like, not just HD which they show off their sets with...