Why plasma? LCD are better as plasma has some sort of life (in terms of hours) and picture quality reduces gradually in few years. Go for LCD, Samsung are good value for money, did you know that Samsung makes Sony's panel (just screen)? So in terms of panel, samsung are the best as they definately keeps the best one for themelves but the processor and the chips are sonys better which means more reliable are the Sony. So if you can pay few hundred dollars more then go for Sony.

For your info: In UK, there is no maket for Plasma anymore.