Unfortunately, picture quality is also the most difficult thing to judge for yourself without actually buying the TV and taking it home (and even then it might be tough!). It's dependent on numerous factors, including source quality, room lighting, and picture settings, that can affect the "true" potential of the TV itself.
1080p: A 1080p HDTV uses progressive scan and has a resolution of 1920 x 1080 pixels. You'll notice the higher definition of this resolution on TVs larger than 40 inches. Many devices support 1080p resolution, so check to see if yours will before you buy a TV.