There is quite a lot to think about when buying a t.v, with the question of LCD or plasma you want to look at what you will be using the t.v for mostly (watching tv, dvds, gaming)
as this will ahve an effect on what tecnology you should be looking at.
With LCD you will use less electricity and have a brighter picture, if your an avid gamer then its prob best to stick with LCD as you wont have to worry about screenburn which you can get when leaving a plasma on a static image for too long.
However LCD is NOT superior to plasma when it comes to movement and black levels so if your not bothered about gaming then you will want to consider a plasma as the picture is crisper and the colours are more vibrant although you will use in some brands up to twice as much power running the tv.
If possible find a store that has a plasma next to an LCD and running a decent picture through it and look at the differences, they are quite noticable.
Average lifespan can vary with brands, if you have no budget and want the best of the best then look at pioneer, they have just released for the 1st time a range of LCD tvs (usually only make plasma screens) although i have not seen one in action yet, knowing the brand they will set a benchmark for other companies to try and get somewhere near, thier plasma tvs are 2nd to none and wipe the floor with any competition and in the year and a half i have been selling tvs i have seen 2 returned with faults, i would expect a pioneer screen to last about 70000 hours.
see next post