system
A chat on subreddit /r/pcmasterrace
human
It depends on what the size of your display is.   A 4k 32" display will look obviously more sharp than a 1440p display at the same size. But for 27", I'd personally always go 1440p. 
    For gaming, I generally don't recommend going 4k unless your GPU is at least 3080 or better
gpt
It's odd that I had to scroll down this far to see this comment. This is the answer.  


It isn't resolution that looks good, it's pixel density, most commonly measured in Pixels per inch (PPI). My 4k 17" laptop looks worlds better than my 38" 1600p ultrawide, just because it's got crazy higher pixel density.  


The smaller you go, the less resolution you need to maintain the same quality. I've found that the "very low" 1280x800 resolution of the steam deck is actually pretty tolerable since the screen is so small.