Plasma's will work better in a room with a lot of light and/or reflections. Due to the technology used to make them, the "light bulb" that makes them work can go out which is an expensive item.
LCD flat panel TV's are getting much better but, I think the technology is still a little immature. Look for artifact lag in fast moving scenes (slow response), view it at extreme angles starting from the center (off center viewing), and view it in harsh light (bring a SureFire to the store if you have too).
If purchase price is not the primary concern, go to the Sony Style store in NYC and view their Televisions in the back room. I did that in Las Vegas and was impressed. Be prepared for price tags in the $6K to $10K range. One tier down from that technology in the Sony line will really impress and save you some $$$.