A 24-inch monitor has the ideal screen size and price. Experts suggest we go for 1920×1200-pixel monitors over 1920×1080 monitors, because a 1920×1200-pixel monitor with a 16:10 aspect ratio will give you more vertical space / taller screen than a 1080p monitor’s 16:9 proportions. 

The best 24-inch Monitor: Dell UltraSharp U2415 (Great color accuracy, multiple connections, factory calibration, highly adjustable, more vertical space than a 24-inch 1080p monitor. Covered by Dell’s Premium Panel Guarantee,, and so Dell will replace the monitor free of charge if your monitor arrives with even one bright pixel defect. But it doesn’t cover dark pixels.)
The second best 24-inch Monitor: Dell UltraSharp U2412M (without factory calibration, USB 3.0, and HDMI)
The best upgrade 24-inch monitor: Dell UltraSharp U2715H (2560×1440 monitor, bigger screen and more working space than a 24-inch, 1200p monitor. More importantly, No app display-scaling issues of 4K 24-inch monitor)
The best affordable 24-inch monitor: Asus VS239H-P (good IPS monitor, 10% less screen space than above Dell monitors but almost half the price. IPS is short for in-plane switching, a monitor panel technology that gives you better color reproduction and more viewing angles)