The 508XD is rated by most reviewers as the best consumer flat screen on the market today.
Its a case of who's views you prefer to give more weight to. A review everything magazine that tries to guide consumers on a wide range of issues, or a specialist AV reviewer like What HiFi who specialise in Home Cinema testing in a £1M specialist facility. I know that WhatHiFi put the 508XD ahead of LCD technology.
In fact I've just put my money where my mouth is and bought the 42" version of the Pioneer.
If you want some more reviews, outside of WhatHiFi:
HDTV Org:
http://www.hdtvorg.co.uk/reviews/plasma/Pioneer_PDP-508XD.htm
"The best HD or SD picture bar none at the price"
Home Cinema Choice :
http://www.tech.co.uk/home-entertainment/tv/tvs-displays/plasma/review/pioneer-pdp-508xd?page=2
"The set is darker, more dynamic than any previous Pioneer plasma and delivers a knock-out blow to comparably sized LCDs. It simply demands to be auditioned."
HDTV Test.co.uk:
http://www.hdtvtest.co.uk/Pioneer-PDP508XD/Conclusion.php
"Although some knowledge and care is needed to avoid introducing artifacts with different source material (for example, wrongly applying film deinterlacing to video content), the 8G Kuro range of Pioneer plasmas has - in my opinion - set a benchmark that leaves other manufacturers trailing in their wake at this moment in time."
Trusted reviews:
http://www.trustedreviews.com/tvs/review/2007/08/11/Pioneer-508XD-50in-Plasma-TV/p4
"Normally we like to counterbalance our praise of even the very finest TVs with a negative point or two. But try as we might, we simply can't think of anything bad to say about the Pioneer's pictures at all. In fact, if it wasn't for the fact that Pioneer is flogging the screen at what has to be considered quite a premium price point, the only problem the brand might have with the 508XD is making enough of them.
I'm not trying to sell you the Pioneer here, only to let you know that most of the reviewers I've come across, don't seem to agree with Which's conclusion.