First and foremost, to ascertain accurate colors, black levels must be deep. My first question would be wether you plan on having the set calibrated. If so, my choice would be with the Pioneer, as its color accuracy and contrast are unmatched when ISF calibrated.
This is not to say that the Panasonic and Samsung models are not good, rather it is to say that the Pioneer PDP-4280HD is better. The Samsungs have improved greatly in the department of brightness and overall contrast, but gray-scaling is still far off from what a plasma should be. The Panasonics have always been excellent plasmas, a "poor-man's Pioneer", as many call it. They are right in this statement. The Pioneers will always outdo the Panasonics with this in mind.
I have seen all sets in question up close, before and after calibration. I can faithfully say the Pioneers attributes are far more favorable than the others, and, what little downfalls it has are negligible compared to the others.
The ELITE has few differences that mark itself different. The front gold lettering, ISF modes (easier for the installer to calibrate), PRO mode (useless if calibrated), a black, backlit remote (handy) as opposed to the silver glow-in-the-dark remote, and Pioneer's two year warranty (as opposed to one for the 4280). At retail pricing, I hardly find this worth an extra $700 or so. But in this market and considering the set's age, you may be able to find it for a significantly lower price. You ask me, I would go for the 4280 unless the ELITE is within around $200 of the 4280's pricepoint.
I implore you to see the reason why I like Pioneers so much by investing in one.