Some of the 1st gen lcd's had a "lag" latency of around 15-50ms. This was somewhat apparent on 1st person shooter games but at that time, the white ghosting was more of a factor than the latency. In modern times the ms delay is in the 2-5ms range from gtg (gray to gray)...youre not going to feel any lag at all.
I have a 4 year old 42" vizo 720p and there is absolutely no lag on it...anything modern thats a namebrand is going to be fine in that aspect. The tv you buy matters, but lag isnt anything thats an issue anymore.
Contrast ratio, resolution, how many hz the screen is, cost, 3d?, those are the issue nowadays ;-)
Whats your budget and what country?