It depends on your situation, how you use it, and the room it's going in.
Plasma produces a "tube-tv" like picture, which most people upgrading for the first time would have an easy time transitioning to. Plasma is a fast technology, and is great for response times when gaming. However, you don't want to leave static (unmoving) imagines on the screen for too long. If you like to pause your movies a lot for long periods, or the kids play racing games where the speedometer doesn't move on the screen for hours, you will probably want to go with LCD. The benefits of plasma are that it's usually cheaper per inch, and the picture is in glass - just like traditional televisions. It also has a faster response time for gamers, although long term, that may cause image retention (or burn-in, as some people call it). The cons are that they are heavier and use more electricity and still images over time will cause damage.
Samsung is also one of the few manufacturers worldwide that makes plasma panels.
LED, on the other hand is lighter, thinner and the picture quality is also great, although LCD is a slower technology. But image retention is not nearly as much of a problem, so you can pause movies and play games longer without worrying about burning in the screen. The LED uses a lot less electricity, and there are more LED televisions to choose from in our 2013 lineup than plasma units. Our flagship models this year have Smart Interaction and gesture control, Quad-core processors and other features, so LED is a popular technology right now.
You may want to have this conversation with a salesperson also, just to get some perspective and in case they have more suggestions that we may have left out here.
But both panels are great, and there's no clear winner in technology since both sell to customers with different needs and preferences. Take a look at the picture quality, the smoothness, and factor in the other points and make the best decision based on your needs. They are slightly different, so if you can't see a difference, don't pay for it. On the other hand, if you can tell the difference, you'll know why you pick the one you pick.
--Mr.Samsung