Theoretically the best balance between high resolution (you can't see any single "normal" pixel anymore at normal viewing distance and normal eye sight) and battery usage is 1440p.
But support for 1440p on Linux (and as far as I know not just Linux) is crap.
Anyway in my experience having a high quality display is much much much more important then the display resolution (as long as it's at least 1080p).
I'm curious what support you think 1440p needs specially or where you think Linux falls down? I've got a 1440p primary monitor for my desktop and the only device to have issues with it is my PS4 pro which only supports 1080p or 4k video out even though 4k mode if often upscaled 1440p
Wayland currently only supports integral scaling, so as long as you don't want the content on the screen to be noticeable smaller (no scaling) or bigger (scaling by 2) you have a problem.
Sure some wayland implementations do support fractional scaling but only in a way which leads to not so crisp fonts and images (scaling by 2 and then down scaling the pixel output to the given 1.x scaling factor), which defeats the whole point of getting a higher resolution screen.
Sure if your 1440p screen is also size wise bigger this might not matter but then my argument was always about increasing resolution without increasing monitor size. E.g. like a 1440p14" Laptop or similar.
Also a perfect size scaling on a 1440p14" to make the UI be the same size as on a 1080p14" monitor is technically impossible, through there are ways to get solutions which are good enough anyway (but not scaling to exactly the same size but something close by, separately for each font and other elements in a UI).
And while X impl. might work better, lets be honest X is dead. Still used, sure, but dead anyway.
But support for 1440p on Linux (and as far as I know not just Linux) is crap.
Anyway in my experience having a high quality display is much much much more important then the display resolution (as long as it's at least 1080p).