Display Enlightment by NCX

*=Perceived black depth increasing matte black or grey (superior) bezel versus fake frame-less monitors perceived black depth reducing inner black bezel.
^=384 zone local dimming which vastly increases the contrast ratio.
+=Variable back-light which vastly increases the contrast ratio.
-Perceived black depth decreasing fake bezel or frame-less casing with an inner black bezel
# Tested by NCX

1.) Acer ConceptD CP7271K *^ (10 bit 98hz 4k, G-Sync, 1000cdm/2 HDR)
2.) Asus PG27UQ *^ (10 bit 98hz 4k, G-Sync, 1000cdm/2 HDR)
2.) Acer X27 *^# (10 bit 98hz 4k, G-Sync, 1000cdm/2 HDR)
3.) Acer Predator XB273K *+ (10 bit 98hz 4k, G-Sync, 400cdm/2 HDR)
4. Acer Nitro XV273K * (120-144hz semi-wide gamut/HDR capable with AMD Free-Sync)
5.) Viewsonic VP2768-4K - (very accurate IPS panel with hardware calibration)
5.) Philips 272P7VPTKEB - (very accurate IPS)
6.) Asus PB27UQ * (accurate with 40-60hz Free-Sync)
7.) LG 27UL550 *# (accurate with 40-60hz Free-Sync)
8.) Monoprice RTD2795 -# (40-60hz Free-Sync & low glow AHVA panel)
8.) Viewsonic XG2700-4K * (40-60hz Free-Sync & very accurate IPS panel)
8.) BenQ PD2700U - (very accurate matte IPS with height adjustable stand)
9.) Philips 276E8VJSB - (very accurate matte IPS without VESA mounts)
10.) Dell P2715Q * (very accurate IPS panel & real bezel)
11.) LG 27UL650  - (40-60hz Free-Sync; 2019 model with slightly faster pixel response times than the UD and UK monitors)
11.) LG 27UD69 - (40-60hz Free-Sync)
11.) LG 27UD68 - (40-60hz Free-Sync)
11. LG 27UK650 - (40-60hz Free-Sync)
12.) LG 27UK600 - (40-60hz Free-Sync)
12.) BenQ EW2780U -

The Acer ConceptD CP7271K is a matte, height adjustable, 3840x2160 AUO AHVA panel with 384 zone local dimming, with 24-144hz Nvidia G-Sync, Displayport, HDMI 2.0, 4x USB 3.0 and 3.5mm Auido Out.  The Acer ConceptD CP7271K has a native 1100:1 contrast ratio (FALD or local dimming disabled), 90.9% DCI-P3 (HDR) and 96.9% sRGB (when the SDR Color sRGB mode is enabled which prevents the over-saturation of non-HDR content) color space coverage, and very accurate color presets out of the box aside from a very minor blue tint and gamma dip at 10% grey.  The CP7271K has a low glow AHVA panel, especially when local dimming is enabled, and fast pixel response times; =DEAD= does not test for input lag, but Tom's Hardware did and measured a 31ms delay versus 36ms for the Asus PG27UQ and 39ms for the Acer X27.

The Acer X27 and Asus PG27UQ are matte 4K AHVA panels with 98hz (8 Bit +FRC / 10 bit HDR 4:4:4), Nvidia G-Sync, height adjustable stand, 4x USB 3.0, local dimming and true HDR color.  Full 4K and 10 bit color (YcBcr 4:4:4) is only supported up to 98hz.  Higher refresh rates requires one to drop the signal from 10 bit to 8 bit (120hz) and from  YcBcr 4:4:4 to YcBcr 4:2:2 (144hz), which results in a loss of clarity, color and text sharpness.  The 384 zone local dimming, gamma shift free and low glow AHVA panel these monitors use allow them to provide vastly superior image quality (especially dark content) compared to all other LCD panels.  Tthe Acer XB273K which is a lower end version with slightly lower HDR color space coverage, lower maximum brightness (400cdm/2 vs 1000cdm/2), and inferior variable back-lighting since the XB273K is edge lit while the X27 and PG27UQ have 384 dimming zones.  According to TechSpot the Acer has slightly better preset color accuracy and lower input lag than the Asus (11.4ms versus 15.6ms), but has slightly slower pixel response times.  Other reviews prove that the Asus is more accurate.

The Acer XB273K has very accurate accurate (SDR/sRGB & HDR color modes; color controls are locked when HDR is enabled) 144hz (achievable only when connected with 2x Displayport cables) 3840x2160 or 4K matte wide gamut AUO HAVA panel which can cover 87.65% of the DCI-P3 color space, provide 460cdmn/2 peak brightness, and can fully cover the sRGB color space to prevent over-saturation when the sRGB mode is selected.  It has a fully adjustable stand, a monitor hood, 1x Displayport, 1x HDMI 2.0, 4x USB 3.0, 3.5mm Audio Out and Nvidia G-Sync.

My rankings prioritize preset color accuracy, low glow and perceived black depth increasing matte grey bezels.  Ranking the non-top 3 monitors is difficult since I have not tested most of them myself and can not determine how much glow they suffer from.  The Philips 276E8VJSB is the best cheap option since it is very accurate, as accurate as some of the 500$+ options and is the cheapest in most countries.  The 27UL550 I tested suffers from minimal glow, tends to be quite competitively priced and supports Free-Sync, but it's not as accurate as the Asus PB27UQ, BenQ PD2700U, Philips 272P7VPTKEB, Philips 276E8VJSB, Viewsonic VP2768-4K, and Viewsonic XG2700-4K.  The Viewsonic XG2700-4K has a perceived black depth increasing matte grey bezel, supports Free-Sync and has nearly perfect preset color accuracy, but uses an older LG AH-IPS panel with more glow than the Acer X27, XB273K, XV273K, Asus PG27UQ 27UL550 and Monoprice RTD2795; I'm not sure if it glows less than the other models I did not mention.

LG UD, UK and UL Series monitors Belgium Hardware Colorimeter and Oscilloscope Measurement Comparison Chart.