A:
Honestly at this point it's irrelevant. Plasma was pretty much discontinued a few years ago.
Both technologies have pluses and minuses. LCD doesn't suffer from burn in or uneven wear while plasma does. LCD uses less power too. Plasma should normally be able to do darker blacks though.
It sounds like plasma got dumped as they just couldn't make them cheaply enough, and then weren't able to easily get them to 4K resolution.