Here's the most educational thing I've read on the subject
https://tonsky.me/blog/monitors/Conclusion
To sum up, this is the best setup for programmers:
- Text can’t be made look good on low-resolution displays.
- High-PPI displays are now a commodity, it’s time to switch.
- Notebooks are ok, but a standalone monitor is always better.
- 4k monitor only makes sense with 2× / 200% scaling.
- If you want to go further, there are now affordable 4k @ 120 Hz options.
My personal thoughts:
I got interested in monitors at the very worst time, which is right after investing in my first nice monitor. It's a 28" Samsung 4K which I'm sure is fully designed with the goal to be the cheapest 4K monitor. I'm mostly happy with it, but here's what I've learned.
TN panels have terrible viewing angles. I used my monitor in an office for a while and if I wanted to show someone something on my computer they could never see anything on it. Not a real problem at home though.
I got a VESA arm and I love it. It saves space on my desktop, looks cool, and allows me to adjust to the perfect position to make up for the bad viewing angles. Even if you don't want one now, get a VESA-mountable monitor for future-proofing. My monitor has the VESA mount holes awkwardly placed towards the top of the monitor so it won't stay in portrait position, so watch out for that.
My impression, having a 1440p Apple Thunderbolt Display at work is that 1440p is probably more of a sweet spot for value these days, but if you're going for the long term 4K isn't necessarily a bad choice. Looking side-by-side you can see why this much older monitor still sells, used, for twice what I got my Samsung for. My advice is to never allow an Apple Display in your house because comparing them will just depress you.
USB-C in the monitor is really nice for a single-cable non-proprietary laptop docking solution, though compatibility can be hairy and there's always docks.