Plasma are cheaper to manufacture but have pretty much come to the end of their development. LCD are still being improved and prices are coming down as the market gets bigger.
I believe Sony are overrated, however they have good and bad products the same with Toshiba. One good thing about Sony, Philips and Toshiba is they invest a lot of money into R&D, bringing out new technology.
Philips CRT and LCD TVs have been winning award after award in the last few years. Doesn't really matter who makes the LCD (most are made by LG anyway) it's how it's driven and the digital processing that counts.