I posted having problems with HDTV lag earlier and I just got a slew full of those useless posts saying "It must just be you"
I will tell you what I know, First Screen refresh rate is only one of many things that can cause lag. Out of the research I have done gamers want 120hz, I dont know much about the physics of refresh rate but you are about to go into something else that causes bad lag, a 768p Tv.
I will try to keep it short. The real resolution of 720p tv's is 1366x768. 720p isnt really used much anymore because 1366x768 fits the tv better. This is where your game system comes in. Plug in HDMI or component and you are only aloud to put out 720p This means your tv scales that 720p to a higher resolution resulting in lag. Some tvs are better than others about processing, but even if you have the best of the best there is lag whether you notice it or not.
So what can you do? Instantly narrow your search down to 1080p, like I said earlier a lot of things can cause input lag and this is no guarantee but its one less thing to worry about.
Take a look at Tv shopping and look at the native resolution of the TVs. They are listed right below the picture on wal marts site
Electronics - Wal-mart