There are numerous differences between the styles of HD-capable tvs.
Plasma
TVs use two panes which hold a gas. Electricity is sent through the gas
which heats and gives you the bright colors that you see (technically
speaking it's much more complicated, but you get the idea). Plasma TVs
tend to be brighter and more vibrant colors because of this. The
drawback is that the heat caused by the plasma can wear out the panes
encasing it, sometimes burning certain colors/patterns into the screen
over time. Also, the plasma itself can lose it's ability to hold the
electrical charge, dulling colors, and eventually burning itself out,
costing you thousands of dollarsafter a few years, either in replacing
the plasma, or buying a new set. I don't recommend plasma in the least.
LCD
as we all know is Liquid Crystal Display. You know, the screen that
leaves the cool little multi-colored wake when you run your fingers
across (which is very bad for it, btw). LCDs are generally
significantly cheaper than plasma, and many DLPs, but operate similarly
to the plasma. LCDs tend to use less electricity to get the same effect
out of their pixels. This still gets you vibrant colors, usually
sharper edges than on a plasma, and a longer life-span, provided
temperature fluctations and roaming fingers don't interfere too much.
Because of technical constraints, most LCDs don't go larger than 36",
as the pixels would need to be enlarged, and consistency and resolution
would suffer drastically. LCDs also have the potential to burn images
onto the screen itself, but you would have to leave the same static
image up for days on end. The pixels themselves can burn out over time,
and if one goes, it could chain to others, but most of the time, you
just end up with a solitary pixel here or there that doesn't work. If
you're not looking for a big-screen, LCD is amazing (I'm using a 27"
for both my computer and what little TV I watch or game on).
Bob
mentioned DLP. DLP is probably my favorite big-screen option. Digital
Light Processors use computer coponents to control a very small mirror,
on which a beam of light is aimed. The mirrors reflect and refract the
light up and onto the screen, where it's displayed normally. Unless you
get one of the higher quality consoles, DLPs have, generally, duller
colors than plasma, but the image is much more defined, uses very
little electricity, and weighs close to the same. DLP sets areusually
built around the same design as the old projection big screens'
self-standing floor sets, but for the most part weigh less than 80 lbs
and are significantly slimmer. The only real drawback to a DLP is
should something happen to the components inside. Be it the mirror
(moving parts) or the computer circuitry that controls everything.
Fortunately, the DLP is generally less expensive than any of the other
HD-capable TVs for it's size. Anything larger than 36" and you don't
mind not being able to stick it to your wall, and DLP is the way to go,
IMO.
HD just stands for High Definition. HD is the new standard of
viewing quality, an all-digital signal with a high potential
resolution, (older TV sets run at about 800x600 resolution, while HD
ratings see things like 1080i, which is essentially about 3-4 times
larger.) Imagine going from 640x480 on your computer, and then jumping
up to 1920x1440. Think of HD in quality increase, as the step from VHS
to DVD. Watch a movie on VHS, then watch the same movie on DVD and
you'll know what I'm talking about.
As far as which to buy, it
would depend entirely on your price range, sense of style, as well as
how and where you'll be using the TV. I would LOVE to have a DLP, but I
don't have the space, or the use for it yet. As it stands, my LCD works
beautifully. There are benefits and drawbacks to each, so the best
advice is to do research on the various brands. Everyone's got their
niche in particular styles. Sony and Panasonic have among the best
plasmas, Hitachi and Mitsubishi produce the best DLPs, Samsung, Dell,
and JVC (IMO at least ;P) put out the best LCDs.