You have to choose the right balance between image quality and responsiveness.
IPS monitors typically look better, but have a slower response time.
How much this matters depends on how much you play games like Skyrim, compared to games like Counter Strike.
For everything except games the IPS are much better, and unless you play twitch games they are better for this as well.
24" monitors have been the standard for a number of years. These will be 1920x1080 or 1920x1200 resolution.
27" monitors have become very popular. Choose a 2560x1440 monitor at this size.
Some good monitors:
Dell U2414H - 24" IPS monitor, 1920x1080, 60Hz (very good image quality, good responsiveness)
Dell U2713HM - 27" IPS monitor, 2560x1440, 60 Hz (very good image quality, good responsiveness)
Asus PB278Q - 27" PLS monitor 2560x1440, 60 Hz (very good image quality, good responsiveness)
Asus VG248QE - 24" TN monitor, 1920x1080, 144 Hz (ok image quality, very good responsiveness)
Asus VG278HE - 27" TN monitor, 1920x1080, 144 Hz (not great image quality, very good responsiveness)
Asus ROG PG278Q - 27" TN monitor, 2560x1440, 144 Hz (Recently released, I haven't read reviews on image quality. Expect it to be better than the VG278QE but not in the same league as the IPS panels above. This monitor only has a single display port input, no DVI, HDMI or VGA)
I have the Dell U2713HM. The color reproduction is just amazing out of the box without any calibration. It also doesn't use PWM back lighting so it doesn't flicker like most monitors.
The fast TN panels are favoured by Battlefield 4 and Counterstrike players. They don't look as good, but the fast response time reduces image blur.
If looking at monitors other than the above, read detailed reviews on them looking at the image quality calibrated and uncalibrated. Brightness and contrast specifications mean very little. The maximum brightness is always way to bright and the contrast figures are taken with screen settings that look terrible.
BenQ also make some popular monitors for gaming, but again these are optimised for responsiveness and the image quality isn't that great.
In a 60 Hz monitor you will not notice a big difference in image blur between a 1ms or 8ms response time. Keep in mind the monitor is only rendering a new frame every 16ms. IPS and PLS panels will have a response time of 6 to 8 ms.
In a 144 Hz monitor this makes a much bigger difference because a new frame is being rendered every 7ms. You will see references on the web to overclocked IPS panels running at 100Hz or more, but the panel does not have the response time to do this well. The true 120Hz or 144 Hz monitors will have response times of 1 or 2 ms, but to achieve this they use TN panels and the image quality isn't as good.