The trick to finding the right general-purpose monitor is getting sufficient display area, contrast, color and features (most importantly, connections) at an affordable price without sacrificing too much elsewhere. Here's my advice on what to consider to get the most for your money.
### Size
All else being equal, if you've got the space and budget, bigger is almost always better. Screen size labeling is based on the diagonal measurement: That made it easy to compare monitor sizes when almost every screen had the same aspect ratio -- essentially the proportions of the screen rectangle, which is the ratio of horizontal to vertical pixels. Wide and ultrawide screens on desktops and newer ratios on laptops (such as 3:2 or 16:10) make cross-size comparisons a little more difficult. You may need to factor in the aspect ratios your favorite games support. If they only offer 16:9 options, configuring them for a widescreen 21:9, 24:10 or 32:9 monitor can be annoying and frustrating; you may also be able to save some money.
If you remember your geometry and algebra, you can calculate the width and height of the display if you also know the aspect ratio. (Because width/height = aspect ratio and width² + height² = diagonal²) The further from 1:1 the aspect ratio is, the wider the screen and more of it will be out to the sides -- and therefore in your peripheral vision if you're sitting close. It will also let you figure out the physical dimensions of the screen, most notably the width, to ensure it will fit in the allotted space.
[DPI Calculator](https://www.sven.de/dpi/) can do the math for you, but keep in mind that the numbers only represent the panel size, not the size of the display, which includes bezels and the mount. Nor does it take into account curved displays, which tend to have smaller horizontal dimensions than their flat-screen equivalent.
### Resolution
Resolution, the number of vertical by horizontal pixels that comprise the image, is inextricable from screen size when you're choosing a monitor. What you really want to optimize is pixel density, the number of pixels per inch the screen can display, because that's what primarily determines how sharp the screen looks as well as how big elements of the interface, such as icons and text, can appear. If you're gaming with a controller at distances further than you'd be sitting at a desk, it can be critical. For instance, I've discovered that I can't read the text well enough to even make it through a tutorial in 1440p on a 32-inch monitor from more than about 4 feet away.
Standard resolutions with a 16:9 aspect ratio include 4K UHD (3,840x2,160 pixels), QHD (Quad HD, 2,560x1,440 pixels) and FHD (Full HD, 1,920x1,080 pixels): You're better off looking at the numbers than the alphabet soup because when you get to variations like UWQHD they can get mind-bogglingly ambiguous. When you see references to "1080p" or "1440p," it's shorthand for the vertical resolution. Examples of widescreen resolutions, which you'll tend to see in 34-inch and larger curved displays, include 3,440x1,440 pixels (21:9) and 5,120x1,440 pixels (32:9).
On a 27-inch display, 1,920x1,080 has a pixel density of 81.59 ppi. On a 24-inch display, 1080p works out to 91.79 ppi. Because a higher density is better (up to a point), FHD will look better on the smaller screen. This also depends on your vision: For me, too low a resolution and I can see the pixel grid and at slightly better than that I see nothing but jaggies on small serif type. So "optimal" really depends on what you're looking at and personal preference. My preference for working, highly detailed sims, games with a lot of text and so on is at least 100ppi; if you're moving so fast there's no time to stop and shoot the flowers, you can probably drop to as low as 90ppi. Once again, the DPI Calculator can do the math for you. (A related spec is dot pitch, the size of the space between the center of the pixels, which is just the inverse of pixel density. For that, smaller is better.)
Because of the way Windows works (and MacOS, too), you're always better off with the highest resolution possible: You can always change the settings to make things that are too small on a high-res screen larger and change settings to increase frame rates, but you can't make things that are too large on a low-res screen bigger.
### Screen type
OLED or QD-OLED generally have the best contrast, color and pixel refresh speeds, although they may have some artifacts on text because OLED's one-pixel-one-color structure doesn't antialias (essentially blur the edges of the characters) as well as the filter array technologies (three-primaries-one-pixel-one backlight) used by other panel types. IPS screens with LED backlights are cheaper but still good -- IPS is the best alternative. If they use Samsung's Quantum Dot technology they have better color, and IPS Black panels have better contrast than straight IPS because of its deeper blacks.
### Color
The bigger the color gamut the screen covers the better. At a minimum, you want 100% sRGB, but 90% or higher P3 (also known as DCI-P3) is best, as it delivers more colors. Look for specific gamut coverage percentages rather than terms like "1 billion colors," which are essentially meaningless because gamut coverage indicates **which** of the "billion" are included. If many of them fall outside the color space you need, they're pretty useless.
If your work or sideline requires accurate colors -- photo editing, video editing, 3D rendering and the like do if you need or want colors to display the way you shot or designed them -- keep in mind that there are various degrees of accuracy, and color management can be an extremely difficult exercise (in other words, if the colors look "wrong," don't automatically blame your monitor). The most popular measure of visible variance from the "correct" color is [Delta E](https://www.viewsonic.com/library/creative-work/what-is-delta-e-and-why-is-it-important-for-color-accuracy/), and the most commonly touted spec is a Delta E of less than 2. That's great for generally accurate color, but that's also an average over a series of color patches. If you need what I call "color-critical accuracy," you really need a maximum Delta E of 2, as well as consistent gray scale. If you plan to output your work for printing, you may also need the monitor to cover more of the Adobe RGB gamut than today's typical sRGB or P3 -- sRGB is tiny and old, and P3 doesn't cover the cyan, yellow and magenta primaries you want for print.
Brightness and HDR
High dynamic range refers to scenes rendered with brighter highlights, greater shadow detail and a wider range of color, for a better-looking image. In order to produce a decent image that looks like you expect HDR to look, you want the monitor to hit a peak brightness of 600 nits (aka cd/m^2) in HDR mode -- you might be able to get away with lower for OLED, but I still would recommend less than 500 nits -- and it's fine if the peak is lower in the standard range, though you still don't really want it lower than 300 for a desktop monitor.
For gaming HDR, in contrast to TV HDR, it means more than just a prettier picture: The better you can see what's lurking in the bright and dark areas, the more likely you are to avoid danger and spot clues and looks a lot better than the black-level boost settings a monitor may have.
And in photo or video editing, even if you don't plan to export as HDR, the greater brightness range provides some useful latitude when you're color grading or adjusting exposure more precisely.
### Ports and connectors
If you plan to connect to your computer via USB-C, make sure the monitor explicitly lists that it supports video out (aka alt mode or video over USB-C). Just because it has a USB-C port doesn't necessarily mean it can get video input that way. And if you want a real USB hub, you should make sure it includes the types of USB ports you need; for instance, a lot of high-end monitors (surprisingly) have an old USB-B 3.0 connector feeding the monitor's USB-A connections, which can be a pain or limiting.
### Price
Unless you can't afford it, assume you'll pay at least $300 (full price, not discounted) for a current-generation model, closer to $600 minimum for OLED and/or decent HDR.