Conversation so far:
what kind of gas is in a tv tube
The cathode-ray tube is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images.
are cathode-ray tubes still used today
Since the late 2000s, cathode-ray tubes have been largely superseded by newer flat panel display technologies such as LCD, plasma display, and OLED displays.

Question: what kind is most common
Self-contained rewrite: what kind of flat panel display is most common