Hi
i have an asus MX279H
believe me i researched all asus monitors from VX and MX and R and all other series the size of the screen in MX model (also known as Designo) are 22 , 24 and 27 inch so you could have 22 model in MX
they basically are the same but the quality of the MX model compare to other series is just about earth and sky.
the price of these two models are nearly same but there are some facts about the MX that you couldn't pass by.
and it's the AH-IPS panel Plus high quality Audio by Bang & Olufsen ICEpower the response time in fact is little slower compare to VX but everything else is just fine.
and tell you something i played ps4 and PC games and watched 1080p movies on MX model the response time is not even a bit annoying and the sound is even better then my sony speakers . the viewing angle is perfect it's exactly what is claimed by ASUS
you could read more in :
23 inch :
http://www.asus.com/Monitors/MX239H/specifications/
27 inch :
http://www.asus.com/Monitors/MX279H/specifications/