Also interested in 70-80" TV here.
Have a near 10 yr old 52" Samsung LCD, never had a problem with it so I'd vouch for a Sammy. Not sure about Sony, we always had trouble with their CRT's for some reason...barely got 5 yrs out of them, probably their led/lcd's are much better (I hope). A lot of people say Vizio is the best bang for the buck, esp on the larger screens. I agree about the OLEDs, great picture but too much of a premium at the moment.