One BenQ XL2420G monitor or 2 Asus VG2A4Qe monitors?

[Lucid]

I have a $500 budget for monitors, and have been looking at the BenQ XL2420G and the Asus VG2A4QE. I play CS: GO alot and other shooters like the battlefield franchise. I like the idea of having a monitor that is great for competitive gaming, and has G-sync capabilities for other games than CS: GO. I am upgrading from A 1200P 60HZ monitor from 2008, so I want a good upgrade. I have 2 of these monitors and love the multitasking I can achieve, but need to upgrade. Should I get 2 of the Asus monitors, or one BenQ?

[Steeps]

Do you game with two monitors? If not, buy one really good monitor since the other won't be used for gaming.

I have a BenQ XL2730Z and a basic Dell 21.5" since only one monitor is used for gaming. Why buy a second equally expensive monitor that is used for Internet browsing or teamspeak?