Plasma TV Advantages
Plasma TVs have advantages over LCD, in the following areas: Better contrast ratio, better ability to render deep blacks, more color depth, better motion tracking (response time), and wider viewing angles.
Plasma TV Disadvantages
However, the disadvantages of Plasma vs LCD include: more susceptible to burn-in (although this is not as much of a factor now, due to technology improvements, such as "pixel orbiting"), more heat generation (as well as more power consumption), does not perform as well at higher altitudes, naturally darker image and screen glare in brightly lit rooms, heavier weight, and more delicate to ship.
LCD TV Advantages
LCD TVs have advantages over Plasma TVs in the following areas: no burn-in susceptibility, cooler running temperature, less screen glare, more functional at high altitudes, longer display life (although improvements are being made in Plasma screen life), looks better in brightly lit rooms due to the ability to produce a naturally brighter image, and less power consumption than Plasma.
Also, LCD TVs have made great strides in upping-the-ante in native pixel resolution, with a majority of sets offering a full 1080p (1920x1080) display capability at affordable price levels in screen sizes ranging from 37-inches and up, but there are some 1080p sets down into the 32 and 26-inch screen sizes. On the other hand, the number of Plasma Televisions offering 1080p native pixel resolution are increasing, but many "budget-priced" sets in the 42-inch (and even some 46 and 50-inch) screen size are 720p sets.
One factor to consider in favor of LCD over Plasma (at least for the near future) is that if you are looking for a smaller screen television, Plasma TVs have not been available in screen sizes below 42-inches for some time now.
One other factor to consider is that LCD TVs are typically lighter (when comparing same screen sizes) than their Plasma counterparts, making wall installation easier.
LCD TV Disadvantages
LCD TVs do have drawbacks in several areas vs Plasma televisions: Lower contrast ratio, not as good rendering deep blacks, has a narrower side-to-side viewing angle, and not as good at tracking motion (although this is improving, especially with the implementation of 120Hz refresh rates (and some now offer 240Hz on higher-end models).
Also, although LCD TVs do not suffer from burn-in susceptibility, it is possible that individual pixels on an LCD televisions can burn out, causing small, visible, black or white dots to appear on the screen. Individual pixels cannot be repaired, the whole screen would need to be replaced at that point, if the individual pixel burnout becomes annoying to you. Finally, large screen LCD televisions are usually more expensive than an equivalent-sized Plasma television, although the price gap is closing.
The Mercury Issue
Also, one argument that Plasma TV manufacturers have made about LCD TV is that some sets still use traditional florescent backlight technology to illuminate the screen surface, and, as such, employ mercury as part of the chemical makeup of the florescent backlight system.
However, this is a "red herring" with regards to choosing a Plasma Television over an LCD Television. The amount of Mercury used in some LCD TVs is not only small, it never comes in contact with the user. Also, keep in mind that most common high-efficiency florescent lamps, such as many used in video projectors, and the "green" lamps we are all supposed to be replacing our traditional light bulbs with also use Mercury.
You are probably in more danger eating fish, that may contain traces of Mercury, a couple of times a week, than watching, touching, or using an LCD TV. On the other hand, with the increased use of LED lighting sources in most LCD TVs made since 2012, which is a Mercury-free light source, this is quickly becoming a non-issue.
For more details on the use of mercury-free LED technology in LCD TVs, refer to my article: The Truth About "LED" Televisions.
One additional aspect of LCD and Plasma TVs that may be a factor in some purchases, is that some 3D LCD TVs use the Active Shutter viewing system, while other 3D LCD TVs use the Passive Polarized viewing system, giving the consumer a choice when considering your preferred 3D viewing option. However, for 3D Plasma TVs, only the Active Shutter system is used. For more details on what this means for your purchase decision, read my reference article: All About 3D Glasses - Active vs Passive.
My recommendation is to go to a dealer and really take a look carefully at several Plasma and LCD televisions and compare the performance based on the above factors and narrow down your choices to one or two of both types and make your decision based on what type will give you the most pleasing image, connection flexibility, and fits your overall budget expectations.
However, both Flat Panel Plasma and LCD TVs are viable options for home theater, and, with prices continuing to come down and features and quality continuing to go up, both types, depending on the features and performance desired, are a good value for consumers