HDTV:
Basic Options:
Resolution: HDTV come in 2 resolutions
1080 (1920x1080) Full HD
720 (1024x768, 1280x720, or 1366x768) Regular HD
Future: Ultra High Definition (UHD) (aka 4K) - 3840x2160

Cable TV and Internet streaming video labeled 1080P is usually compressed so you are not getting full 1080p.
BLu-ray disks are full 1080p
DVDs have a standard definition resolution of 480 or enhanced definition resolution of 520.

Screen painting: Most are p=progressive. Old i-interlaced (odd lines are painted followed by even lines) are less common.
See 1080i vs. 1080p: What's the Difference? | PCMag.com
1080p is termed "full HD" or "true HD,"

Many people are perfectly happy with 720p HDTV sets even at higher sizes;

Smart TVs:
Smart TVs have WiFi and support internet video from services like Huuu and NetFlix.
See Internet TV

Some also have web browsers built in.
Samsung has a wireless keyboard you can use with it.

Miracast and DLNA
Some new TVs have Miracast and DLNA technologies. Miracast is a standard that lets you wirelessly "mirror" content on a portable device, such as a smart phone, tablet, or laptop, on your TV. The Digital Living Network Alliance (DLNA) supports a standard that enables interoperability among various consumer electronics devices across a home network. A DLNA-compliant TV can access photos, movies, and music stored on a DLNA-enabled PC or smartphone through a network connection. So if your phone is on your wireless network, you could view photos you shot or received via e-mail on your TV screen.

Picture-in-picture (PIP)
This lets you watch two channels at once--one in a small window, the other as a full-screen image.

Screen Size:
Most consumers would be best served by at least a 40- to 42-inch screen for a primary TV. A 46- or 50-inch set is often preferable in rooms where you'll be sitting 8 to 10 feet or so from the screen. Consider an even bigger set for spacious family rooms.

Typical prices (end of 2014) for sets with good ratings:
60" $1,100-$3,000
50"   $500-$1,500
40"   $350-  $550
32"   $250-  $400

Links:
LED TVs 2014: Reviews and Prices | rtings.com
LCD TV and LED TV Buying Guide: Reviews, | lcdtvbuyingguide.com
Top TV Reviews | Best TV - Consumer Reports
TVs - CNET


Old 2007 Post here:
HDTV is broadcast in two flavors: 1080i (interlaced) and 720p (progressive).

Newer HDTVs are 1080p with 60 fps, so can display both formats as well as high-def DVDs from Blu-ray and HD-DVD players.

It is commonly stated that 1080i looks better up close, but from a normal viewing distance--about 6 feet from a 42-inch screen--a 1080p set won't look dramatically better than a good 720p TV.
The High Definition 1080p TV article at HomeTheaterHiFi.com explains the advantages of 1080p.

As of July, 2007
Type Display Size price * weight
(lbs.)
Flat Panel LCD 40-57" 47" $1,600-2,800 47" 55-65
Flat Panel Plasma 42-58" 50" $1,800-3,200 50" 85-105
Rear Projection DLP 50-65" 57" $1,800-2,700 57" 75-85
Rear Projection SXRD 50-70" 60" $2,700-4,000 60" 92-112
Rear Projection CRT 47" $1,900 47" 147
Front Projection 110-300" 1080 $4,000
720 - $1-2,000
15-24
* Price is for the specified size screen or resolution (for Front Projectors)
- 768p LCDs are available in smaller (20-42") sizes.
- Projection TV's are deeper (15-16" vs 4-5") so usually need to be floor standing.
- Front projectors require an external HD tuner, such as a cable or satellite box. For movies, you can hook up just a standard or high-definition DVD player ($250). - Front projectors are able to go up to 300"

720p - 720 lines of resolution progrssive (lines are painted in sequence)
1080i - 1080 lines of resolution interlaced (odd lines painted first 1/60 sec,
    even lines 1/60 sec.)
LCD - Liquid Crystal Display
DLP - Digital Light Processing
LCoS - Liquid crystal on silicon
SXRD - Silicon X-tal (Crystal) Reflective Display

Flat-panel TVs: LCD - Plasma:
LCDs (Liquid Crystal Display) use a matrix of crystals which act like a shutter, either allowing light to pass through or blocking the light.

Plasma TVs usa a matrix of gas-filled cells. A grid of tiny electrodes applies an electric current to the individual cells, causing the gas (a mix of neon and xenon) in the cells to ionize. This ionized gas (plasma) emits high-frequency UV rays, which stimulate the cells' phosphors, causing them to glow the desired color.

Plasma sets used to be the only flat-screen TVs larger than 40 inches, but LCDs now come in big sizes too. With the price gap between plasma TVs and big-screen LCD sets narrowing, more buyers are choosing LCDs.
Plasma sets have a wider viewing angle, slightly more lifelike color.
LCDs are generally brighter and less prone to glare than plasma and not prone to screen burn-in.
Plasma has a reputation for being less efficient, but tests at the Washington Post with a power meter didn't bear that out: The Panasonic Plasma used about the same amount of electricity over an hour as either LCD - though the Philips plasma drew about 25 percent more juice.

Projection (Front and Rear) TVs: DLP - SXRD - LCoS:
SXRD (Silicon X-tal (Crystal) Reflective Display) is a new technology from Sony is a refined variation of LCoS (Liquid Crystal on Silicon). SXRD is a "reflective" technology that sandwiches a layer of liquid crystal between a cover glass and a highly reflective mirror-like surface patterned with pixels. While LCD is a "transmissive" technology where light passes through the image chip Reflective displays such as LCoS and SXRD (and DLP) use the light from the TV's projection lamp more efficiently, resulting in higher picture brightness and contrast.Reflective displays such as LCoS and SXRD (and DLP) use the light from the TV's projection lamp more efficiently, resulting in higher picture brightness and contrast.

Trueness of color is also one of the significant differences between two major types of projectors: LCD, for "Liquid Crystal Display", or DLP, for "Digital Light Processing". DLP projectors tend to be very bright with higher contrast ratios, and they have become popular for smaller, lighter, "ultra-portable" projectors. To produce a color image, DLP projectors reflect a light through a rapidly spinning color wheel, which can lead to a slight flickering of color (called a "rainbow effect") and sometimes to an unnatural color appearance. Many newer DLP projectors now use faster-spinning color wheels, which can reduce the effect or 3 chips to eliminate the wheel.
LCD projectors often do slightly better with color, but they tend to shift the color a bit towards the blue range, and some significantly so.
DLP projectors also run very hot, which can be a problem for a portable projector in particular.
Due to the relatively high switching speed of DLP (up to 1,000 times faster than some competing technologies), DLP-based systems can more accurately display dynamic images (e.g. sporting events), while technologies with slower response times may produce some image smearing. For more information about DLP, see: www.ti.com/dlp.

LCoS "Liquid crystal on silicon" is a version of LCD technology, used by companies like Sony in high-end models. Compared to LCD, LCoS pixels are closer to each other, producing a smoother image and eliminating the screen door effect (a grid pattern on the screen) generated by LCD projection.
As of 2006, there was no consensus on which technology was best.

Bulbs on rear projectors have to be replaced on the average of every 6,000 hours while front projector bulbs last for 2-3,000 hours.

Front projectors can create an image up to 300" diagonally, howerver the larger the image the dimmer it will be. Consumer Reports found that 110" was the optimal size. For that size, you'd typically place a projector 10 to 15 feet away. The optimal viewing distance is 14 feet or so away from the screen -- about three times the height of the display area.
Image quality is just as good as that of plasmas and LCDs, However ambient light tends to wash out the picture.

You can get HMDI cables up to 39' (12 m.), longer cables may require a HMDI repeater.

Projectors require a screen. A 110-inch screen that has a matte-white viewing surface 4½ feet high by 8 feet wide will cost about $400. Or you can use a wall treated with special paint (such as Screen Goo). There are screens with more reflective finishes (called gain) designed to enhance brightness, but they might have a narrower viewing angle than a matte screen. So-called dark screens are designed to enhance contrast by improving black-level performance, but they see a small decrease in overall brightness.

See: Projector Screens

Front projectors will also require a receiver/amplifier for the sound.

Connection Ports - Video Interface - Connections - Inputs:
High-definition video comes in via two connectors: digital HDMI (high definition multimedia interface) and analog component video. Get a TV with two of each kind, plus a VGA (analog) or DVI (digital) port if a computer will be plugged in.
(You can get DVI to HDMI conversion cables/plugs.)

Reviews:
ConsumerReports _
cnet
PC Magazine

Reliability at CR
Percentage of brands that needed a repair or had a serious problem. 2.g. 2 = 2% had problems, 7 = 7% had problems. Differences of less than 3 points aren't meaningful,

Hitachi 2
Panasonic 2
Emerson 2
Sansui 2
Dynex 3
Sony 3
Sharp 4
Philips 4
TCL 4
LG 4
Seiki 4
JVC 4
Sanyo 4
Insignia 4
Haier 4
Samsung 4
Element 5
Magnavox 5
Hisense 5
Vizio 5
RCA 5
Westinghouse 6
Sceptre 7

Black Friday Deals ?:
The surprising reason you can't find good TV deals on Black Friday - TODAY.com Nov., 2015 Claims many of the black Friday deals are derivatives sold only on black friday. Check that out with the model number if it only shows up on black friday sales it is probably a derivative minus some feature(s) or sub quality. The best time to buy a TV is super bowl sales getting rid of old for the new TVs.
Most of the deals are on large screens.

Links:
LCD, LED, & OLED TVs Ratings & Reliability | Consumer Reports (Requires subscription)
Projector Screens
Audio-Video
Video Resolution
Home Theater and A/V at Crutchfield
Best TV Buying Guide - Choose Between HD and Ultra HD – Consumer Reports
HMDI cable benchmark
High Definition 1080p TV: Why You Should Be Concerned

last updated 4 Jan 2015