Higher resolution monitors, such as those with 4K or 1440p resolutions, offer more pixels, resulting in sharper and more detailed images.
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If you expect to be able to render your games at above 60 FPS too, a high refresh rate 4K monitor (at speeds like 120Hz, 144Hz, or even 240Hz) is a good one to opt for, although that combination of technologies tends to get inordinately expensive.