A good 120hz monitor can really make games (especially FPS) a lot more crisp. However, keep in mind that when looking at picking one up that you require more GPU power in order to push the FPS for an enjoyable gaming experience.
As far as which monitor is for you all depends Response Rate
The response rate of an LCD monitor refers to how quickly each pixel on the screen can change color. The lower the response rate, the faster the screen updates. If you are playing fast-paced action game for example, where the images change quickly, if you're playing on a monitor with a slower response rate, you may experience what is known as "ghosting". Ghosting happens when the previous image displayed on the screen can still be seen as a blur for moments after the image has changed.
When choosing the best gaming monitor, the response rate is perhaps the single most important factor to consider. Ghosting and motion blur can ruin your overall gaming experience. The faster the response rate of your monitor, the less ghosting you will see.
I would say that an LCD with a response rate of 5ms is the minimum for gaming. Lower than 5ms is better of course (remember that the lower, the faster), and the very best gaming monitors on the market have extremely fast response rates such as 2ms and lower to avoid any ghosting/blur issues completely.
LED vs LCD Monitors
LED monitors are the exact same as LCD monitors, except they use LED backlighting which provides some advantages such as a brighter and sharper display, thinner screen, and lower power usage.
LED monitors currently cost a little more than a standard LCD, but if you want the best gaming monitor then I would definitely suggest you buy one. If not, a standard LCD monitor with a good response rate will do just fine.
What Size Monitor?
Ultimately, the size you go for is totally up to you and how much you're willing to spend. Obviously the larger the screen, the more expensive it will be, but for the best gaming monitor experience I would suggest at least 19", and go for a widescreen LCD if you can. Nothing beats gaming on a nice, decent-sized widescreen monitor.
If you want the most immersive gaming experience possible and you have the money to spend, go for a quality 23" or 24" screen, or even 25" and above. After gaming on such a massive screen you won't ever want to go back to a smaller screen!
The contrast ratio of a monitor can be a helpful spec to generally compare picture quality between different monitors. In general, the higher the contrast ratio, the better the picture quality.
With high contrast ratios your screen can produce deeper black levels, which creates a more immersive and visually sharp experience. Keep in mind that the contrast ratio isn't always an accurate measure of image quality, so don't use it solely to compare two monitors as there's more to it than that.
If you look at an LCD monitor from an angle, you will notice that the image appears dimmer and the colors can look weird. At extreme angles the entire image can even disappear. The viewing angle of an LCD monitor is the angle at which you can still view the screen clearly, and is usually listed in the monitor's specifications list.
The greater the viewing angle, the better, but for gamers the viewing angle doesn't really matter because you are looking directly at the screen the whole time. But there are some people who will consider the viewing angle important, for example if you need to show presentations with your LCD monitor.
Matte vs Glossy Screens There are two kinds of modern LCD screens: matte (anti-glare) and glossy. Both have their pros and cons and are a subject of many discussions.
Matte screens don't get glare or reflections on them; however, the same rough surface (polarizer) that reduces the intensity of reflected light results in less contrast and brightness since the light from the LCD screen has to pass through it. Matte screens diffuse light instead of reflecting it so they might be easier to read outdoors, if the backlight provides enough brightness. You don't have to worry about reflections unlike with a glossy screen. One of the downsides of a strong anti-glare coating in matte displays is a grainy "crystalline" pattern which is mostly visible when viewing text on a white background.
Glossy screens have vibrant colors and high contrast and brightness because they have a smooth, high-gloss surface. As a result, it is often the choice for movies or gaming. However, strong lighting sources in the environment cause glare on these screens which is not only annoying, but can also cause eye strain and pain. If the lighting isn't adequate, you will also see distracting reflections on the screen. Some graphics designers may find the colors inaccurate, although that mostly depends on the LCD matrix. Glossy will work great for you if the lighting in your room doesn't create any glare on the screen. 120Hz
Why a 120Hz Refresh Rate Computer Monitor?
120Hz Vs. 60Hz
120 Hz vs. 60Hz Refresh Rate - Source: BenQBoth response time, the time it takes for a pixel to go from black to white and back again, and input lag, the difference in time that it takes for you to input a command into your computer and see it displayed, are very well-known terms in the gaming community. Few gamers think about the impact that a higher refresh rate will have on their game.
What is Refresh Rate?
Refresh rate is basically the amount of times in a second that a monitor will draw the data which it receives. Most TN and IPS panel monitors have a 60Hz refresh rate. In order to really see all the advantages that come with a 120Hz display you should be gaming at an FPS well above 60.
Benefits of 120Hz:
1. Details are more crisp, smoothly rendered, and lifelike.
2. More Responsive