The ASUS ROG Swift PG279Q and the ASUS ROG Strix XG27AQ are both excellent gaming monitors from ASUS's Republic of Gamers brand. One of the biggest differences is that the PG279Q has native G-SYNC support while the XG27AQ is simply G-SYNC compatible. That said, the XG27AQ has faster response times at max refresh and especially at 60Hz, resulting in exceptionally clear motion. While the PG279Q has a marginally higher contrast ratio, the XG27AQ experiences less backlight bleed resulting in more uniform blacks, which is good if you prefer to game in the dark. That said, black uniformity can vary between individual units. The XG27AQ also supports HDR while the PG279Q doesn't, although its HDR experience is a bit lackluster because it doesn't get very bright for HDR content.