I think the most important thing when buying any TV is how it looks to you both picture and aesthetics
As I said above how a TV processes colour and motion is really important
There are generally two main resolutions available to LCD buyers: 1366x768 (720P) and 1920 x 1080 (1080P) plus a whole plethora of resolutions for plasma. I don't sell plasma anymore but if I was buying one I'd be looking at either Pioneer or Panasonic and a minimum of 1280 x 724.
It kind of depends what your planning to watch on your set. If its Blu-Ray disc and above 40/42 in size I'd get 1080P.
If you're watching DVD,Sky digital/HD and/or Freeview HD I'd be looking at some bargain 720P panels that are out there particularly if you are going to buy 40" or below in size.
Watch a lot of sport and DVD then plasma is probably for you. If you're into TV and gaming then LCD may be better particularly for smaller sets. Bigger sets are cheaper in plasma than LCD.
One other thing because 1080P sets have twice the amount of pixels as 720P ones they have to be able to process turning on and off all those pixels that much
better.
Some brands do it very well some appallingly badly.
Have a look around. Ask to watch Freeview HD on the set as well as DVD and remember a lot of chain stores crank the colour and contrast right up to attract your eye.