There's an emerging picture standard that offers four times the pixels of today's high definition. It's known as ultra-high definition, or 4K. But do you need it?
Measure the distance between your couch and the spot for your new TV. If you're sitting far away, a regular HD set will be just fine.
The farther away you sit, the less the extra pixels matter, as your eyes won't notice the difference. Conversely, the bigger the screen you have, the worse the resolution will be, and you'll notice that more when you're closer up.