Televisions - LCD, LED or Plasma which is"better"?

Ok, I have a big box tv that has reached the point that several times a week I have to slap it up across the side of its box to get it to come on so I think I will be in the market for a new one shortly.

What is the big difference between the LCD, LED and Plasma flat screens and is one any better than the other or is it really worth the extra money to choose one over the other?

I watch way too much tv as it is but do not see me changing my lifestyle any time soon so I am wanting something that will sate my urges without costing more than it is worth.

Probably looking in the 47” to 50” range.