Now the iiyama with an IPS panel will probably have better colors than the AOC with a VA panel.
The AOC is curved, the iiyama straight. The question is what you like better. The response times are MPRT values. The question would be how it looks with GtG, which is not stored anywhere, at least on the large pages.
The AOC has FreeSync, the question is whether you want to use it and has a graphics card that supports it.
Otherwise, I would assume that the iiyama is slower and has more input lag with an IPS panel. There are relatively few models that are really interesting for gaming, like the more expensive LG UltraGear's.
In general, I wouldn't recommend any of them. 1920x1080 at a 27 inch resolution is scary little DPI. Normally, with a 27 inch device, you tend to take something with a resolution of 2560x1440p.
With 27 inchers I would rather orientate myself on the following models:
https://geizhals.de/...1_25601440
There you have a resolution of 2560x1440p, at least 144 Hz and 2 ms GtG as response time. The rest is then a matter of taste (Curved vs. Flat, TN vs. VA vs. IPS, whether FreeSync or G-Sync or neither, etc.)
