Hey man,
TL;DR at the bottom. I've been looking into the specs you've listed and dove a little deeper. ViewSonic has released a newer model this year with similar but better stats. It's called the ViewSonic XG2705-2K, has a 1ms response time instead of a 3ms response time and the monitor stand is adjustable in height, pivot, swivel and tilt, as opposed to the VX2758-2KP-MHD's tilt-only. The only other differences I could find are marginable (the newer model has 4 Watt speakers, but I'm assuming you won't be using those).
The Gigabyte G27Q seems good on paper, but the 1ms specification might be false advertising, some people are mentioning a higher response time (around 6ms) instead of the advertised 1ms. It also has an OSD menu which takes some getting used to and also has a external power brick that seems to have some coil whine (buzzing noises). It also has an 8-bit panel instead of all the other monitor's 10-bit panels. I don't have a personal experience with the difference between those, but if I'm to believe the internet, it's supposed to be much more immersive/look a lot better.
There are other options, like the Acer Nitro VG271UP, but I can't really recommend it. The panel seems to be alright, but it lacks some features in other areas and the monitor stand is only tilt-adjustable and it lacks a DisplayPort cable.
The only really viable option is the Lenovo G27q-20, another monitor that was released this year, is a bit cheaper where I live, has a 165Hz panel (as opposed to the other monitors' 144Hz advertised refresh rates), but seems to have some IPS bleeding and glow issues.
Here's your TL;DR: All in all, I feel that the newer ViewSonic XG2705-2K is the safest bet if it is in within your budget. It's the monitor I would get personally but I can't really find any reviews on it. You could give the Lenovo G27q-20 a go, since it seems to be the best bang-for-the-buck monitor, but the IPS bleeding/glow issues could annoy some people. If the two monitors you've mentioned are your only options, the ViewSonic monitor is definitely the one I'd go with.