Each has its strengths and weaknesses. I work with six other technicians in a consumer electronics repair workshop. My observations led me to settle on LCD for my TV, but not without some consideration and observation of similar products before settling on a slightly unusual choice based mainly on perceived image quality.
Reliability: Plasma has proven to be less reliable than we would like. Overall, LCD is less trouble-prone, as might perhaps be expected from generally good service life of LCD laptop screens and monitors. Generic faults that can affect either type tend to be magnified in plasmas as they have higher power consumption and higher operating temperatures than comparable LCDs. We've certainly seen screen burn on plasmas. Recent screens are less susceptible than earlier generations, and it would require serious periods of static screen images to cause permanent burn-in. LCDs can experience some image retention, but unless a screen is actually faulty, it is temporary. Both can experience pixel faults such as bright or dead pixels. LCDs can also experience pixel bleed (permanent black patches where the liquid crystal bursts from the cells), and various types of mura, which is an optical aberration such as discoloration of the light guide behind the panel. But overall these are rare. Neither panel is as resistant to impact as a CRT, and can be smashed by a flying Wiimote.
Power consumption: Plasma for a given screen size has noticeably higher power draw than LCD. This will be more significant with the rise of LED backlighting, which is more efficient than CCFL (Cold Cathode Flourescent Lamps). Heavier power consumption of course hits the pocket in power bills, and also means the TV runs hotter, heating the room and not helping with reliability of the electronic components. Some units are cooled with internal fans, and this can annoy some people because you can hear them during quiet viewing.
Screen size: Plasma has traditionally exceeded LCD in the maximum screen size available. If you must have the largest you can get, then it will probably have to be plasma. Don't get a screen that is too large for the room size. If your eyes can resolve individual pixels from the normal viewing position, the picture will look bad.
Motion blur: Pixel transition time has been an achilles heel of LCD, with plasma and CRT technology having a shorter persistence characteristic. Long persistence leads to a blurry trail behind the path of fast moving objects, and is one reason to consider plasma if you watch things like sport and action movies. LCD has improved considerably in this regard and current generation screens can cope well with fast movement. But it's still one reason we advise people to see the screen they are considering in action displaying fast-moving material, unless they are unconcerned about this aspect of its appearance.
Image "quality": This is a general term - personally I find a good quality LCD screen more pleasing than a similar quality plasma. One thing to look out for is called "clay face", and its name describes the effect - faces in particular look artificial, as if sculpted from wet clay. More recent designs have been less prone to it, and its complete absence was one factor in my own choice. Keep in mind that the perceived quality of an image can be affected by various processing options offered by most sets, and the settings for sharpness and other types of dynamic processing will alter how "good" the picture looks. The maximum resolution of the screen will also affect the amount of detail that can be presented, with a 1080p (progressive scan) rated unit required for full high definition. Of course this affects the price accordingly.
Brightness: An LCD generally gives a brighter picture than plasma, and will cope better with brightly lit rooms, sunlight etc. This is one reason an LCD is often recommended for general duties as a replacement for a CRT TV. The reverse is true for low levels of illumination and low brightness images. LCD suffers some light bleed through "black" (ie turned off) pixels, whereas a plasma pixel turned off to give black produces no light at all. So the plasma looks much better in low-light situation like home theatre, and when displaying low-brightness images like dark movie scenes. For this reason, plasma is the standard recourse for home theater, or if folk use TV mostly for the movie channel or DVDs. LCD has made considerable improvements here too, and pixel-based modulated LED backlighting may close this chink in LCD's armor too, but at a price.
The future: For a while there have been indicators plasma may be on the wane. Some strong supporters of the technology have backed away - AUO (an original innovator of the TV technology) ceased plasma panel production some time ago, Pioneer intends to leave the TV market within 12 months, and there is speculation LG may also intend to cease use of plasma panels for its TVs. High power consumption technologies are expected to face increasing pressure to reduce energy consumption, especially in Europe.
In the end, the choice must be made by the user. You'll be watching the screen hopefully for many years, it's you who needs to be happy with what you've chosen.
If people ask us at work, we advise people to see several prospective sets operating with the type of material you watch, and as close as possible to the viewing environment the set will be used in. Due to the high possible repair costs (particularly for plasma) outside of warranty, a long warranty period is a consideration. For this type of product, purchasing an extended warranty can also be worthwhile, but check exclusions - the panel itself (the highest cost item that you would really be glad of cover for) may be excluded, or certain types of panel failure not covered.
Again, in general, for taking over the duties of a household CRT TV, probably running for long hours with some movie/DVD viewing, consider LCD. For more serious movie watchers, home theatre etc, look to plasma. For Wii/computer, try some and see which you prefer.
Edited by Platypus, 02 April 2009 - 06:31 AM.