Hi, Let me make it simpler for you to understand. Plasma tv's are known for reference level picture quality, something which all tv's aspire to reach. The BEST tv's in the world are plasma tv's unmatched in picture quality. However they are best suited for low light or dark room conditions.
LED, on the other hand are extremely bright and best suited for very bright rooms. Some of the hi end LEDs are now getting better and can almost match plasma's in certain aspects of picture quality.
Here's my pick:
Plasma
Samsung 64F8500 (my pick) - the only bright plasma also suited for brighter rooms with reference like picture quality.
Panasonic 60S60 - budget level plasma, excellent value for money, performs much better than many similar priced LEDs
LED
Samsung F8000 - Samsungs best LED, almost as good as the F8500, avail in 55 and 65 inches.
Samsung F7500 - lower down, very similar picture quality like F8000 but for a lower price. Excellent value for money. Available in 55 inches.
Sony W900 / W800 series - giving Samsung serious competition. Priced lesser than Samsung. Available in 55 inches.
You can go lower down in the series for Sony/Samsung but if you have the budget these are the tv's you want to check. Please demo all the ones possible and then decide. Suggest to demo various video content right from HD to SD.