Before making a decision on make and model check out one of the viewing distance/screen size calculator sites.
http://www.engadgethd.com/2006/12/09...o-screen-size/
http://www.crutchfieldadvisor.com/S-...me/tv_faq.html
Initially, plasma sets are the best all around display. They do not suffer from LCD lag, viewing angle drop off, backlight color change or DLP illumination failure. However, they do form a smoke like film on the interior of the glass over time and they are subject to burn in like most displays. They are also the heaviest of the bunch.
Newer versions of the LCD family have less lag, better back lights and better viewing angles. As many have reported, the Vizio line is a good buy. They do not make the display but they are manufactured in the US. The Sony XBR line is very good looking, has almost true blacks and a color correcting backlight for accurate colors. However, it was recently reported to me that Sony no longer manufactures their own sets. Samsung is producing them for Sony. No details on whether that applies to all Sony sets or not. I suspect the same goes for other manufacturers.
DLP makes a nice picture and has few of the issues that LCD displays have but a much higher price tag on the illumination device. If considering a DLP ask what the replacement cost for the bulb is and whether it can be replaced by the consumer or requires a factory service call. A friends DLP has a great picture but there is something about the display that I have a problem with. It may be the over compression of his cable system.
No matter what you buy, you will be subject to the the compression and resolution decisions of the provider. Even over the air broadcasters do not broadcast in full HD 1080i most of the time. Those that choose either 1080i or 720P still can heavily compress the signal to allow other services to use some of the 19.2Mbit spectrum stream which reduces the bandwidth of the main signal. These compressions are mostly visible in motion, such as waterfalls, rain, car races, sporting events, backgrounds of seascapes, etc.
Be aware that when viewing a signal in a store, it could be playing back from a video server in the backroom, off the air or from a cable provider. Even if it is an HD signal, it could be upconverted from a standard def program.
I should also note that Plasmas generate of lot of RF noise. Although newer designs are better, if you require a quiet RF environment then one of the other technologies is a better choice.