I do not currently own a plasma or any large screen display so I have no dog in this fight.
I have been looking closely for some time and have some observations.
When I began looking a couple of years ago, it was RPTVs and Samsung colors no matter how adjusted just were not right, whites always had a yellow or golden cast. This past year, however, they improved markedly and their DLP color is now excellent along with their outstanding case asthetics.
About a year ago, as I got interested in plasma, I noticed Samsung seemed to have processor problems and their pictures exhibited all sorts of artifacts. Recently I have had the priviledge/opportunity to spend some time with a couple of current xx73 model ISF calibrated Samsung displays. The PQ on these did not exhibit any of the bad artifacts I saw a year ago.
So I have observed with my own eyes that Samsung is improving very rapidly.
Are they perfect? No. I have noticed on several current models too much overscan that cuts off more picture than other brands. I don't much like this characteristic. Perhaps there is some setting that can change this? I don't know. I also noticed a tendency during action, such as basketball players breaking for the net, for the players to break up a bit as if the processor could not keep up with the action. I noticed a similar issue with the Panasonic sitting to one side of the Samsung but not on the Elite to its other side.
So for anyone that thinks Samsung cannot show aceptable shadow detail I suggest you find an ISF calibrated set and look for yourself. The BB on the East coast have a 50" Samsung ISFed and thus adjusted the Sammy looks the most natural of all the displays in the store. Samsung is sure improving rapidly.
I also liked the clarity, depth, and naturalness of the Panasonic picture on still and slowly moving scenes once I could adjust it. OOTB it is horrible. But on action, the picture lost its clarity. I am eagerly awaiting this year's new Panny processors.
I could not get hold of the remote for the Pioneers and so could not make the adjustments necesary for a comparison. As they were, the picture was too soft and the colors exagerated.
My top pick at the moment for a 50" plasma would be the NEC for its superior processing, features, and reliability.
P.S. Samsung is introducing a new and improved line in April. It may be worth waiting for. They are particularly working on black levels using new filter technology.