I think Samsung and LG are essentially identical in terms of quality and philosophy. I'd consider them to be "The Sony & Panasonic of Korea," both formidable competitors, both capable of making good and bad products, both out to make a lot of money.
I kind of blame the Korean manufacturers for the downslide in prices and picture quality over the last 10 years, but in truth, that happened for a variety of factors, and they're just among many causes. And I have seen some top-of-the-line sets from both that were calibrated and looked very good.
One issue with getting an extended warranty on a plasma at this point is that if the plasma fails a year from now, there's a good chance they won't be able to fix or replace it with another plasma. I still like plasma very much, but even I admit we're kind of at the end of that road.