My gf parents have a 450 series Samsung plasma that looks fantastic from what I can tell. Truth be told, whatever you decide on will be great because once you get it dialed in and watch it for awhile, it will look awesome. I went from a plasma to an old rear projection gigantoid TV and after a week of viewing the projection TV looks great to me. Maybe not as good as the plasma, but it really does the job well.
The Samsung has a pixel shift feature that shifts the image on pixel at a time to prevent image burn in. I'm sure the panny has it to, but I don't know for a fact. Anyway its a cool feature and imperceptable from a distance