Lovely to see companies like Samsung promulgating confusing technology nomenclature. What they and nearly everyone in this thread are referring to as "LED" TVs still use an LCD panel to form the image, they just use LEDs arrays for the backlight. Conventional LCDS have a fluorescent backlight. The difference is primarily that you get better colors with an LED backlight LCD. In the near future, local-dimming LED backlit LCDs may provide near-CRT black levels, but possibly at the expense of losing details in darker areas.
I agree with dickbutt up there that plasmas are probably still the best bet for the time being if you're after the absolute best image quality. Plasmas have superior black levels and contrast ratios vs. LCDs (LED backlit or otherwise), though not quite to the level of a good CRT. They also don't suffer picture degradation at off-axis viewing angles like LCDs do. However, burn-in is potentially an issue. Oh, and plasmas are nothing like normal TVs, for whoever said that, except perhaps in terms of black levels and off-axis viewing. Otherwise, they're completely different technologies.
One interesting technology that provides what is probably the best image quality you can currently buy is Mitsubishi's Laservue. It's a rear projection DLP-based display that uses lasers as the light source in lieu of a conventional lamp. The reviews say that it results in some of the most vivid colors and detail you can get. It's also significantly more energy efficient than LCDs or plasma (and therefore runs cooler). The downsides are that it's rear projection so it's not as slim as LCD or plasma, and suffers a bit from off-axis viewing (typical of rear projection). It's also more expensive.
So to summarize:
LCD (conventional backlight): good picture, average power consumption, slim, average price
LCD (LED backlight): basically the same with a bit better picture
Plasma: better picture, black levels, off axis viewing, may use more energy/run hotter
Laservue: best picture, best power consumption, not slim, off-axis viewing suffers a bit, most expensive
OLED: will probably have the best picture yet, still a couple years out, will be expensive initially
edit: I want to add that the quality of all these display technologies is at such a high level these days that really only videophiles are likely to notice the difference. If you're asking a question like "is LCD or plasma better?", then go ahead and buy that LCD you saw at the big-box store. Just pick whichever one looks good to you, because it'll more than likely be good enough for you.
