1920 x 1080 on a 21.5" screen is a bit small for me so my 1st choice would be the Samsung P2350.
I don't like the Asus MS228H because it seems to sit pretty low on the desktop. Granted, none of the monitors have height adjustments, but... I just don't like the design.
If you want a monitor with LED backlight, then I would go for the Samsung BX2231. However, some people notice that they types of monitors have colors that look a bit bluish. This is because LED backlit monitors have a color gamut of 68% rather than 72% normal color gamut. Wide color gamut monitors are approx 96%+ and colors tend to bit a bit more greenish, but the benefit is for color printing which makes matching the printed colors to what's on the screen easier to calibrate.
You may or may not notice the slight bluish colors of a LCD monitor with LED backlight. The benefits are lower power consumption, and the monitor can be made thinner than a monitor which uses traditional CCFL backlight (florescent).
Additionally is the monitor being used for professional work or for school?
These inexpensive monitors that you have chosen use TN panel technology which means the colors are not very accurate. If color accuracy is important then none of the monitors will provide it for professional use. However, money is a major concern for most people so if you can't come up with more money, then there's no point in talking about more expensive monitors.