Ultimately the differences between the better models of both plasma and LCD are so negligable as to be completely irrelevant to the average person. If you are a magazine reviewer then you will pick up on some of the subtle differences but to be honest for everyday TV viewing the source picture is what dictates what you see rather than the quality of your screen.
I am sure that there are AV'philes on here who will disagree with me, but in their own world they are as geeky and territorial as we woodies are about the way in which we do things.
I have a 42" panasonic Vieira plasma which is 4 years old and a 50" Samsung LCD which is 12 months old and next to each other, with the same source, the picture is nigh on identical. The Panny deal slightly better with high speed action as the LCD can 'ghost' ever so slightly, but until I pointed it out to the missus she hadn't even noticed it, so it's definitely not worth worrying about IMO.
As Tom said, if you are looking for HD then the sound is equally if not more important than the picture. You really need to consider what you want from it and if you are looking for the full HD experience then you really need look at the following:
- TV
- HD box (SKY HD etc)
- BluRay player
- AV Amp/Receiver
- External speakers
Now there are myriad ways in which you can do the surround sound piece but it can be done relatively cheaply and to good effect with all in one systems, or you can go all out and spend a couple of grand. Again, it all depends what you want to get out of it.
Just to clarify, I don't work in this field and am no expert, but it is a personal passion and I have spent a lot of time over the years setting up my own and friends systems so if you want the benefit of my years of tinkering (I won't say skills, that would be over selling myself
) then I am happy to have a chat if you want my number.
HTH