usually pag sinabing HD 720p yun, pag HD ready mga 720p (or less) din, ang full HD is 1080p
sa hertz, refresh rate yan, higher refresh rate better results. merong 60hz, 120hz, and the newer 240hz
kung luma ang mga gadgets na ikakabit mo sa tv (i.e. dvd player, NAS, home theater) then you will need more AV input slots BUT if bago what you need to look for is HDMI, SPDIF, or even USB