Refresh rate is king. I would much rather use a 1080p 120+Hz monitor over 4k 60Hz. 1440p 144Hz is the sweet spot though, big visual improvement over 1080p without the need to bankrupt yourself on a GPU powerful enough to drive a 4k 120Hz display or relying on upscaling making everything a blurry mess.
Refresh rate is king. I would much rather use a 1080p 120+Hz monitor over 4k 60Hz. 1440p 144Hz is the sweet spot though, big visual improvement over 1080p without the need to bankrupt yourself on a GPU powerful enough to drive a 4k 120Hz display or relying on upscaling making everything a blurry mess.