If you intend to watch TV while dry camping, then a 12 volt TV might be best.......but it will pull your battery down. My 15.6" TV DVD combo pulls 3.8 amps, so a 20" would probably pull more.
You would need to get a properly sized inverter if you bought a 120 volt TV and used it while dry camping, and I understand there is some power loss using that, so that might use more of your battery power than a like sized 12 volt TV.
If you dry camp and want to use the TV, make sure there is a nearby 12 volt supply receptacle.
If you never intend to dry camp, then a 120 volt TV is probably your best bet.
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263