The difference between LED and Plasma (in terms of Picture Quality) is not that much anymore, as long as you get a good LED TV. The main things you'd be after in an LED that you won't get in a Plasma is energy efficiency, as well as good viewing in a bright environment. If it is a well-lit environment, you will benefit from the LED screen, as the panel in a plasma is glass, which reflects light quite well. If it is dark, a plasma generally performs better than an LED TV, though LED's are also great in the dark.
In terms of refresh rate, plasma TV's generally have a much better refresh rate, which result in good viewing of fast-moving objects, like sports. Most higher-end LED's have around 200hz refresh rate (which is excellent), though most high end plasma's have around 600hz or more. Of course, whether you can tell the difference between something being refreshed 200 times per second and 600 times per second is something that may come into play. In short, plasma is better for refresh rate, though the higher-end LED's are more than enough, especially for general TV-show viewing.
In terms of "white" whites and "black" blacks (ie, contrast ratio), both will perform well. The older-style LCD TV's had a problem with giving white whites and black blacks, but that was fixed in the LED tvs. Plasmas, on the other hand, are excellent with their contrast ratio.
You'll find as well, that most Plasma's will run a fair bit warmer than an LED tv (as they consume more electricity, and as well as the way the Plasma's actually output the colour) as compared to the LED (which uses LED's inside, hence the name).
Most importantly, when setting it up (slightly unrelated), the optimal viewing distance from the TV is about 3x the screen size. So, if the screen is 55", try to sit around 165" from the TV. This is, of course, a guideline, but it is best for eyesight and visual tracking of everything on the screen.
> Good for energy use > Not-so-good for energy use
> Great contrast ratio > Excellent contrast ratio
> Great refresh rate > Excellent refresh rate
> Great in light or dark rooms > Great in dark rooms
So, for what you're after, an LED would probably be better, but, read over this and make your own decision. No-one knows what you want better than you do!