Ok, here ya go.
Plasma and LCD both have distinct advantages and disadvantages.
Plasma:
+ Pure blackness levels, they are able to turn off pixels. Because of this, it is said they have better contrast, due to deeper blacks. This is the only reason they have better contrast, however. You don't get a "better picture" with plasma.
+ Better viewing angles
- Plasmas suffer from screen burn in, an affliction not as commonly associated with LCDs
- Use more energy in general than LCDs
- Plasma TVs are heavy and more difficult/dangerous to mount
- At larger sizes, Plasma cost more than LCD, generally
Myths:
1. Plasma pundits will tell you that some LCD screens have a tendency to blur images, particularly during fast moving scenes in movies or in sports. While that was true for older generation LCD screens, newer models have improved significantly -- so much so that the differences in performance between LCDs and plasmas in this regard is almost negligible (here's a tip -- if you're shopping for LCDs, check the pixel response time, measured in ms. The lower it is, the better the image quality in fast moving scenes).
2. Traditionally, the biggest advantage plasmas have had over their LCD cousins is price, particularly in the large screen end of the market. In the past 12 months, this has changed, with LCDs matching or even beating plasmas in both resolution and price.
LCD
+ LCD's tend to have a higher native resolution than Plasmas of the same size.
+ LCD's tend to consume less power than Plasma TVs
+ LCD's are lighter and easier to mount
+ LCDs have a longer lifespan than plasma screens, LCD's are guranteed for 60,000 hours, Plasma tend to average 30,000.
- Tend to have worse viewing angle
- Can't show pure black, due to inability to turn off pixils, thus plasmas tend to have better contrast ratios.
Myth - LCD's have slower response time than Plasma. False. Explained above, repeated in case you missed it. Most LCD's from decent brands, like Samsung(the best brand) are made with gaming in mind.
A bit on contrast ratio. The numbers aren't regulated. Therefore, they are only useful for comparing TVs within the brand you're choosing from.
Zenfoldor's advice:
Get a LCD.
It lasts longer, it won't burn in your health bar from Bioshock on the top of the screen and ruin your TV, and it's at a higher resolution for cheaper. LCD is the mainstream TV. Plasma just isn't.
Plasma will have a better picture(all things being equal) due to its ability to turn off pixels making them completely black. However, usually all things aren't equal. Like with all TV's a cheap plasma is still crap and will look like it up next to a good LCD. In the store, you're probably gonna go straight to the series 4 Samsung LCD's when you just pick which ones look best.
Screen burn-in isn't as bad now as it once was, and it's no longer permanent, but it still exists, and in fact, most gamers who own plasmas, do get temporary burn in everytime they play. Games are actually designed with burn-in in mind, now. However, it's not as noticable or permanent like once was.
Your TV will lose half its life, that's a certainty. Plasmas, all things being equal, don't last as long as LCDs.
As for resolution? You're going 42" I suggest 720p. You'll never need 1080p, at that screen size, and you'll never notice the difference. Trust me.
As for a TV to recommend to you?
I recommend the Toshiba Regza LCD 42" 42hl67. I have a 1080p model for my living room, and for the price, the 42HL167 IS the best TV. I'd assume the 42HL67 is just as good, but you'll want to get some reviews. I'm pretty sure you can get that set for under a thousand bucks fairly easily, and I'm talking about the 1080p model.
/bow