Right now, Plasma TV's offer the highest picture quality on the market theoretically.
However if you are buying a TV, my recommendation is to definitely go with an LED-LCD.
Plasma's are dying out quick and will be off the shelves quite soon. LED-LCD TV's offer a picture that goes toe-to-toe with plasma's (the good ones), however it weighs a fraction as much, it produces a fraction of the heat, it is a fraction of the thickness, it takes up a fraction of the power, and is immune to burn-in (plasma is not).
Therefore in my opinion, LED-LCD TV's are superior to Plasma. (New Laservue and OLED TV's are better but aren't really available and come at a cost unnatainable for most on the market).