LEDs are LED back lit LCDs and come in three forms. The cheapest and most widely available are edge lit, next are the full LEDs that cost a fair bit more and then theres the RGB LED sets that arent available for the home market (as far as Im aware).
Only benefits of edge lit realy is cost of running and they're thinner. They have the same issues as normal LCD with worse uniformity due to the lights being on the edges of the screen and can have worse clouding.
Full LED back lit sets have better black levels using local dimming. These sets can produce a good pic but are still LCDs so have the same issues.
RGB LED sets have coloured LEDs rather than the common W-LED used in the others, producing more accurate colours.
Im no expert but I know enough to prefer plasma over LCD.
LCD has viewing angle issues, blur with fast motion, uniformity issues, can have back light bleed, most have higher lag, black levels arent as deep as a good plasma and they have less shadow detail.
LCDs cost less to run, go brighter, are thinner and sharper than plasma and better for bright rooms due to matt screen and brighter image.
Plasma can get IR, cost more to run, some can see flicker and phosphor trails, not so good in very bright rooms, are bigger and heavier.
Plasma gives better motion, deeper blacks, more shadow detail, decent sets have more accurate colours out the box, lower lag, better SD IMO, higher contrast.
Im being quite general and its late so prob missing some things. Sets can vary a lot though generaly plasma is still seen as having better PQ for the money. Checkout the review section to learn some of the pros and cons.
Whats your budget by the way? also if you didnt know, the new sets are due out in the spring, so maybe worth waiting.