1080p vs 1440p vs 2160p

Solution
Depends what your hardware your willing to invest in, both VIDEO CARD ---- AND Monitor. You can have the most expensive card, but still only output 1080p because the monitor you have only supports it. Also it isn't just resolution (1080p, 1440p, 2160p) but MHz of the monitor that matters. Linus did a whole bunch of Youtube videos discussing all this, and you can check them out, but the break down is like this.

4K: People toss this around mistakenly because they confuse store TV Demo 4K with Gaming 4K. 4K has TWO parts: SIZE (resolution or how many pixels are built into the monitor) and Rendering (of models and textures for gaming). There is many simple pictures to show you 'big' a 4K size screen is as compared to a very small (1/4...
Really depends on your video card. If your running below a 1060 6GB or rx580 you should stick to a 1080p. A rx580 ro 1060 6GB can either be highend 1080p or low end 1440p. The 1070 or Vega 56 1440p75~100Hz. The 1080 or Vega 64 can be either high end 1440p or lowend ultra wide 1440p. The 1080ti highend 1440p, ultra wide 1440p, or low end 4k.
 
Depends what your hardware your willing to invest in, both VIDEO CARD ---- AND Monitor. You can have the most expensive card, but still only output 1080p because the monitor you have only supports it. Also it isn't just resolution (1080p, 1440p, 2160p) but MHz of the monitor that matters. Linus did a whole bunch of Youtube videos discussing all this, and you can check them out, but the break down is like this.

4K: People toss this around mistakenly because they confuse store TV Demo 4K with Gaming 4K. 4K has TWO parts: SIZE (resolution or how many pixels are built into the monitor) and Rendering (of models and textures for gaming). There is many simple pictures to show you 'big' a 4K size screen is as compared to a very small (1/4 sized) 1080P normally is you see. To make a PC push 4K size screen takes ALOT of power, and is limited at this time to the GTX 1080 for frame rates above 40FPS consistently. 4K Rendering: In the TV Demos the 'video' is already recorded to a Blu Ray, CableTV, YouTube, etc. data file and thus is just 'read' as it is and displayed already 'generated' (aka rendered) for the 4K detail level that makes it look amazing 'real' (aka SoapOpera effect). Computers/Consoles have to CREATE aka RENDER the models (the frame the textures lay on) AND the textures to make it look like those TV Demos, and that is VERY VERY difficult to do with 'playable' FPS level. Both together is beyond except the most Ultimate Gaming systems.

1440 : Again people mix this up, while you can have a 1440 sized screen because it is WIDE SCREEN, this does NOT generate 144FPS / 144hz on the screen. Hz on the screen makes alot of difference when you 'take it away' as compared to when you see it. The difference is how many more frames of information is stuck in each 'scene' you see in comparision to make those split second decisions, and accuracy where your not shooting where you THOUGHT they were because your not seeing all the 'information' inbetween to KNOW where the person is to shoot at them, thus 'missing' or not registering what you thought was a hit. Again LINUS did a bunch on this and the difference your brain picks up to 'see' as compared to (60hz normal screens) the stuff it is trying to 'fill in the gaps'.

1080P : The standard of video now, and normally a 60Hz screen that any modern hardware can easily provide.

UltraWide: Advantage to this is for people whom are multi using their screen, for example working on three seperate documents at the same time side by side. The size of the screen isn't 'larger' it is 'longer', and also still needs enough 'power' to generate that much info across the entire screen.


Cheap answer: Any Walmart cheapo Monitor and a onboard video provides this minimal basic to watch Netflix, view webpages, etc. without issues. Not for gaming

Mid answer: 1080p monitor with a decent dedicated GPU, GTX 1050Ti to 1070 to provide consistant 45-60FPS on AAA titles using High graphics (1070 can push Ultra).

High Answer: Dedicated GPU GTX 1060 to 1080, higher end monitor Ultra Wide 144hz screens, constantly 60FPS High to Ultra performance in AAA title games.
 
Solution
22-24" : 1080p with an RX580 / GTX 1060
27": 1440p with Vega56/64 / GTX1070/1080
28-32": 4K Vega64 / GTX1080/Ti

Depending on your budget or size preference. 1080p and 1440p can also give you high refresh rates (120/144/165Hz).