There are different panel technologies like IPS, TN and VA, and sub-panels such as S-PVA, S-MVA, S-IPS and H-IPS. In general, an IPS panel (and variants) is considered to be the best if you favor color accuracy and viewing angles above all other things. IPS monitors used to be pricey, but that has changed considerably in the last three years. For example, a 24-inch, LED-backlit IPS monitor can now be had for around $400; just a few years back, that same specs would set you back at least twice as much.
For gaming monitors, a TN (twisted nematic) panel is usually used because of its fast pixel responsiveness. The true response times of the best TN panels today range from 2 to 5ms. In general, the faster the pixel responsiveness, the less pixel trailing or 'ghosting' effects you'd notice during action sequences. For 3D gaming, we feel that the larger the 3D monitor, the more enjoyment you'd get from the visual depth that 3D brings. And let's not forget about connections. If you want to connect your game console, Blu-ray player, or notebook to the monitor, you need to ensure that the latter has the proper ports. The majority of monitors now come with at least one digital connection, be it DVI-D, HDMI, or DisplayPort; the better (and more expensive) ones would come with several. Naturally, you should also check what connections your graphics card is able to support before buying the monitor.
The Acer S235HL is a 23" wide LED monitor, with a resolution of 1920 x 1080, a contrast ratio of 100M:1, and a response time of 5ms.
The S191HQL is the most affordable from Acer at Sitex 2011. It's an 18.5" wide LED monitor, with a resolution of 1366 x 768, a contrast ratio of 100M:1 and a response time of 5ms.
The Acer GD245HQa is Acer's highest-end model showing at Sitex 2011. The 23.6" wide 3D monitor is full HD with a resolution of 1920 x 1080, a contrast ratio of 80000:1 and a response time of 2ms.