DEFINITELY the 50PH10UKA. The 5053 has nice-looking specs on paper, but is actually not such a great display... and the last-gen Panasonics from the same time period crush it in pretty much every way imaginable (colors, black levels, contrast, processing, reliability, etc.).
If you want a 50" plasma that's cheaper than the Pioneer 5080 (and don't need speakers/stand), the 50PH10UKA is the next best thing, IMO. It should offer slightly better PQ and better build quality than the Panasonic consumer line, and offers more adjustments that a good ISF calibrator can take advantage of.