The Samsung is a regular 60Hz monitor. The Asus and Acer are 120Hz monitors.
Never seen a 120Hz monitor, but people say it provides smoother and higher frame rates. Between the Asus and Acer, the Asus is newer and "looks better" (not a big fan of orange) and is cheaper because of free shipping. Otherwise, their stated specs look similar.
The benefit (for some) of the Samsung px2370 is that is has an LED backlight (a low-end LED backlight reduces color accuracy, but also draws less power, generates less heat, and usually allows the monitor to be thinner and lighter). The s23a950 will have an LED backlight and support 120Hz. If you want both LED and 120Hz, I suggest you wait a bit to find out if the s23a950 is affordable for you. If it isn't, your other choices will hopefully still be available.