that the Samsung has better blacks than most LCDs or if he (or she, don't want to be sexist) is saying that it has better blacks than the Panny.
If you meant the latter I can tell you right now that that is false. The Panasonic has better black levels than the Samsung. Unless your talking about an off brand Plasma like a Vizio, plasmas almost always have better blacks than any other TV technology aside from CRTs.
As far as the original poster's question about which is the better TV, I would go with the Panny.
Plasmas are best for movie viewing because of their unbeatable black levels. They also have great color saturation, are very bright (though not quite as bright as LCDs) and have great uniformity. Not to mention the best viewing angles.
If you were using the TV for gaming more than anything else, it might be a closer call because of the burn-in issue with plasmas. Burn-in can be avoided by taking advantage of the sets own burn-in fixes as well as properly breaking in the set, but it is still more of a hassle to deal with than with an LCD where burn-in is not even a slightest bit of an issue. But since you are looking for a TV that suits your primary need of movie watching, the Panny is better.
Not to mention bigger. Four inches may not seem like a lot, but you will appreciate all the real estate you can get when you are watching movies. If this is your 1st WS HDTV, you might be surprised to learn that movies will still have black bars at the top and bottom of the screen. Movie WS is different form TV WS. TV WS comes only in 16:9. While there are some movies that are shot in 16:9 aspect ratio, and will fill your screen completely, many are shot at higher aspect ratios like 2.40:1, and will consequentially have black bars.
Also, since you are getting a 1080p set, you will also like the TV to be as big as possible to take advantage of the extra res (50" may not even be big enough to be honest depending on how far you sit from the screen).
And don't listen to the uninitiated that will try to convince you that plasmas don't last long. Newer plasmas last up to 60,000hrs or about 20+yrs of 8hr a day TV watching.