A 4K monitor with a high refresh rate would likely be overkill if your rig has an older graphics card, and for those cases, the BenQ Mobiuz EX240 is the best budget 1080p monitor at the moment.

The ultra-high refresh rate, paired with low latency ... Colors should look vivid and accurate, with the monitor covering 95 percent of the DCI-P3 color space and 100 percent of sRGB.