Given a $500 USD budget, and photography use, I would suggest getting a 27" monitor that has
- UHD 4K resolution (3840x2160 pixels). (Or 2560x1440, if you prefer … but you can run a 4K monitor in Retina "looks like 2560x1440" mode for the same text size, with a greater level of detail)
- An IPS panel, for wide viewing angles with a minimum of color shifts
- 100% or near-100% coverage of sRGB. If the monitor specifications do not mention sRGB, this is usually a sign that the coverage is not very good.
- One or more modern inputs: DisplayPort, HDMI, and/or USB-C (DisplayPort). (Many third-party monitors have at least two inputs, and at least two types of inputs, which can give you more flexibility for how to connect them to your current computer, and increase the odds of being able to reuse them with your next computer.)
Optional:
- 100% or near-100% coverage of a wide gamut – Adobe RGB, DCI-P3, or both.
- 10-bit-per-channel color depth
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Some manufacturers to consider might be Asus, BenQ, Dell, ViewSonic, and Dell. You may have to filter through a lot of monitors on each site to find ones in your price range with the features you are looking for. E.g., on the Asus site, there seemed to be two 27" UHD candidates: the $399 ASUS ProArt Display PA279CV (100% sRGB), and the and the $499 ASUS ProArt Display PA279CRV (100% sRGB, 99% DCI-P3, 99% Adobe RGB). But an unfiltered list of all their monitors (regardless of size, resolution, features, or price) might have had something like 200 entries.
