I was going to post the same as the above post. If you want a really good gaming monitor, a BenQ, Asus, and certain other select models in all the other builders, in 144hz, is a good way to go. 144hz instead of 60hz means you can see up to 144 frames per second instead of a max of 60. Many will say that the "eye can't tell the difference" between anything over about 30, but trust me, anyone who compares a good 60hz to a 144hz side by side, or even within a short period of time of using either, will tell you that 144hz looks much better, particularly with games. I know in AH, I would never, ever go back to 60hz again.
Gsync is ok, but IMO, honestly, it's really not worth the extra $, which is a lot, to get a Gsync monitor for Aces High - certain competitive FPS games, it can make a difference, and there IS a difference and improvement with it, but I would never advise anyone to get it unless they had excess $ or $ was no object. A good 24 or 27" BenQ or Asus 144hz monitor (that gives you 4 to choose from right there) should be within 300 on the low end, and 400ish on the high. The last Asus linked by 38Ruk, I've had 3 of them in the last couple years, as well as the 27" version, and only recently upgraded to a newer 27" 1440p 144hz monitor from them. In truth, the 900$ I spent compared to the 279$ you can get the 24" Asus for - not really worth it, so you're better off with the 24" anyhow IMO. Best $/buck performing monitors I've had, the VH248QE.