Yes picture is better on LED in comparison to LCD, if you have the money go with LED. If not LCD is still fine.
Most important to me is the option for 120 Hz (or 240 Hz) and Motion Interpolation. Love the way things look with that feature, I know some people don't. But Last year I was buying an LCD TV I went with a smaller TV with 120 Hz Motion enhancement rather than a bigger one without that feature for the same price.
I've personally never been a fan of Plasma, I watch TV during the day and get a lot of light into my living room, so it wouldn't even be that great of an experience.
As for the difference between Blu Ray and DVD. Thats HUUUGE, I converted practically 100% to Blu ray a little over a year ago, and I'm never going back. The difference is really IMMENSE!
When prices go down some, I'll make the leap to 3D technology!