In short: brightness, contrast, and refresh time.
Brightness is measured in Candelas per square meter, or cd/m2. A typical figure, for instance, might be 500 cd/m2. More is always better, especially if you plan to plant your TV in a bright room where the screen will have to overcome other light sources.
Contrast is measured as a ratio of the brightest white a TV can produce, over the darkest dark. For instance, Insignia’s NS-L42X-10A offers a 4,000:1 contrast ratio. More is also better, but beware of “dynamic contrast ratios,” which use unrealistic measurement conditions (the brightest white is measured with the backlight set to full, and the darkest dark with the backlight to minimum, even though those levels could never occur side by side on the same screen) to inflate the number to levels like 2,000,000:1.
Refresh time is measured in milliseconds, such as 5ms. Lower is always better, and will prevent the “ghosting” that can sometimes be seen in fast-motion video.
Many of the top television manufacturers – including Sony, Sharp, Panasonic and Samsung – include Ethernet jacks on the back of their premium televisions for high-speed Internet connectivity (or in some cases, have integrated Wi-Fi for wireless connections). TV viewers will then use the remote to select “widgets,” graphical icons on the screen that plays relevant (and customized) content ranging from YouTube videos and Flickr photo galleries to local weather, news, sports updates and stock quotes, usually delivered by Really Simple Syndication (RSS). Even more exciting is the partnership between Netflix and various TV companies, such as LG and Sony, allowing television viewers to access tens of thousands of movies on-demand, many of which are in high-definition.
If you plan on watching, free, over-the-air programming, then yes. As of 2009, all over-the-air broadcasts use the ATSC standard. Pretty much all HDTVs manufactured over the past few years will include this feature.
A final consideration when buying a new HDTV is what you can connect to it. Make sure there are ample HDMI (High-Definition Multimedia Interface) ports to connect multiple components, such as a cable/satellite receiver, video game consoles, DVD/Blu-ray player, camcorder, and so on. At least three or four such ports is a must. A convenient bonus is when the TV also offers a USB port to connect a Flash thumb-drive or external hard drive full of music, photos and videos, or a SD or Memory Stick card slot that lets you insert a compatible card that contains photos and videos. If you think you’d like to connect your computer to the television for big-screen web surfing, look for one with PC connectivity. Many TVs today offer these additional features.