A 2560x1440 monitor running at its 1:1 native resolution. The screen real estate improvement over 1080p is substantial. You get so much more vertical space and you can easily fit 4 side by side code windows at 80 chars. At 24" or 25" the PPI is also quite nice for reading text. I wrote up a very big monitor selection guide at https://nickjanetakis.com/blog/how-to-pick-a-good-monitor-fo... , I try to keep it up to dat…
People keep saying this but I don't.. see.. it. Everything scales great on my setup. I could make one letter cover the entire screen if I wanted to - the DPI is not really relevant in that sense. You still have to set size up to your liking. And I do not have great eyesight (contacts/glasses).
Admittedly, DPI does play a part when you have multiple monitors with different resolutions. I have solved that by wrapping my launcher with a script that detects the screen, reads the DPI and scales accordingly. Which, to be fair, is not something you should expect people to do :p
My desktop uses an LG-27GL850 and an LG-27GN950. One is 1440p, the other is 4k. Both are 144hz. I first bought the 1440p, which is great, then I bought the 4k one. I wanted to keep the 1440p one for gaming, but as it turns out, I don't game, so I regret not getting two 4ks.
I did extensive research before getting these, and after a year with them side by side, I can for sure see the difference when I read text. The fonts (and everything) just pop more.
I would be completely fine with 1440p, that looks great as well, but since I am at my computer for the better part of my life, a few extra dollars was (and still is) worth it for me.
PS: 144hz was almost weird at first - the cursor and scrolling is so instant. Highly recommended.