Get a name brand LED LCD and use it with an inverter. None of the 12v DC TV's are built well and are made as cheaply as possible in China, branded and sold in the USA under a variety of names. I would buy Samsung, Sony, and Toshiba and expect reliability and reasonable warranty coverage.
The LED type of LCD displays will use the least amount of power for their size. The larger the set the greater the power draw and faster the TV will drain your battery bank and the more weight that the mount will need to support.