I personally don't own one of these TVs, but by an odd coincidence my parents happen to own both of them. I have spent a bit of time watching their Pioneer PDP-5071HD and their XBR1 Sony (so it's last year's model), and I would personally choose the Pioneer simply for its better SD performance. Neither of these TVs does a great job on regular signals, but the Pioneer seems markedly better at it. Also, if you have any plans for gaming on your TV, I would be wary with the Sony model. The XBR1, at least, lags with video games, whereas the Pioneer does not.
If you are more concerned about HD programming, however, the slight edge should go to the Sony for its 1080p capabilities (assuming you're looking at the new KDS). I also find the user menu on the Sony to be more robust and easier to navigate than Pioneer's.
I can't find serious flaws with either of these sets, so its really a toss-up. The HD picture on either set is top notch, they both have generous connectivity, wide viewing angles, etc. No matter which you choose, you will be getting a superb machine.
(Warning: If you choose the Sony and this set is used frequently by other people, make sure they are okay with such a huge TV. My mother grew to dislike the Sony purely for its size, and that's why they also have the Pioneer.)
I am buying a new tv soon and am considering one of the two tvs I mentioned above. I am looking for about a 50" display and I know these sets are quite different but I was wondering if any of you have a strong opinion one way or the other.
With the plasma I can save space but I know the Sony has more performance capabilities. Does anyone own either of these two sets?