The 3rd one is best. Although the 2nd one does have a 2ms response time, for gaming a 5ms response time is fine. But the 5,000,000:1 contrast ratio of the 3rd one really puts it ahead of all the others.
Contrast Ratio: This is a spec you should probably ignore, because it's often inflated (especially with TN panels). Although, extremes can indicate a difference in panel technology, or that one panel has dynamic contrast. A dynamic contrast measurement is sometimes denoted with the "(DC)" suffix or "DFC" prefix. Some manufacturers offer real and dynamic contrast figures, both of which are usually inflated.
1080P is 1920 x 1080 resolution.
The difference in size, 21" vs 22" vs 24" at 1920 x 1080 just means that the pixels or dots that make up the picture are bigger with each increase in size. For a desktop viewing distance it does not make much of a difference. If the monitor is a quality unit with no dead pixels, they will all be about equal. Lesser quality units may accept several more dead spots before deeming the unit to be defective.
How do you plan to handle sound? If your needs for sound are modest, look for a monitor with integrated speakers. It makes for a cleaner desktop. Such sound is OK. If you will be buying a good speaker system, then don't pay anything for included sound.
Do you possibly want to use the monitor as a TV? If so, look for a TV tuner included.
As to specs, the only one I find to be very important is the viewing angle. Better monitors will not wash out the display when viewed from a side angle, or elevation. These monitors are 170/160 horizontal/vertical. Very typical and OK. The very best and expensive units will be 178/178.
A lcd will refresh at 60 hz. That is once every 16ms. If the grey to grey change is 2ms or 5ms, It should not make much difference. Also, different manufacturers measure differently, so you can not put much faith in these particular statistics.
The best would be to go to a local store and look at different monitors yourself. The color tone or other factors may make a big difference to you.
I don't mind about the integrated speakers and TV. I am looking for good value, either quality or large monitor. Are integrated speakers basic? I usually use a monitor for general use, HD videos and gaming. Right now, I stuck into this offer