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 AOC Gaming C27G4ZXE is the best budget 1080p monitor at the moment.

AOC has introduced the Q27G40XMN in the Chinese ... offering smooth and responsive visuals for competitive gamers. The monitor is equipped with a Fast VA panel supported by a 4608-LED backlight ...