Both are excellent choices, but the Panasonic will give the best performance. I actually bought the Samsung without research at a local store due to its sale price. While I was waiting for the delivery, I decided to do some research on my new TV. Overall, expert and user reviews rated this tv very good in overall value and performance. It has 3 hdmi and PIP, which the Panasonic model does not have.
I also read consumer reports about Plasma VS LCD pros and cons of both. After looking at all tv reviews and ratings, the TH-50PZ700U came out on top as the best performing tv in all the catagories. Consumer reports actually said it the highest rated HDTV ever, which says alot coming from these guys. That's what prompted me to exchange the samsung for the panasonic. I'll be paying 2.5k for a tv so I want the best.
Given your viewing environment viewing from 14' is very far for 50' tv. 8-10' would be ideal for this sized tv. Both tv's will have glare as panny is a plasma and this samsung model glares alot for an lcd. The samsung is also 30 lbs lighter if you are considering to mount w/o professional help.