Do you want streaming functionality?
The bdt500 offers this the pioneer doesn't , also the bdt500 I would think offers better firmware support.
found this-
Anyone done a test of this vs the Pioneer LX55? Looking to buy but not sure which one? I have the pioneer LX55 Amp so thinking matching it with its stablemate but any info on which delivers best sound/picture for films appreciated.
I tested them side by side (using a Pioneer receiver, incidentally); they're roughly on a par for performance, but the Panasonic edges it, especially with DVD upscaling. Plus it loads discs much faster and has a ton of smart features. On flip side, Pioneer has SACD and DVD-A support, if that matters to you.