Personally, I'd recommend the LG panel before the other two. The BenQ has gamma issues, and cannot be calibrated to standard gamma settings since BenQ has chosen to incorporate their own "idea" of what gamma should be set to (But other than this, it's an excellent monitor) and it does not have G-sync but it does have G-sync compatible Freesync.
The Gigabyte panel has some contrast issues, so if you are very picky about black colors being black, rather than some shade of dark gray, this might be an issue. This would be especially obvious if you tend to game or watch video in low light or dark situations, and less likely to bother you if you are normally using it in a very well lit room. Regardless, I don't like blacks that are gray. For me, it's a deal breaker, but it's also not uncommon on IPS panels. For this reason I tend to gravitate more towards VA panels, which these days look every bit as good in most cases aside from very expensive models, as most IPS panels, but generally have much better contrast and very good response times.
For me, the bottom line is that I like the LG panels, in general, better than most of the competition out there. LG has become a leader when it comes to displays and if we're being honest I'll say that I currently have three identical LG 1440p panels and have had them all for about five years with zero issues. Every BenQ display I've bought has died or started having problems almost immediately after the one year warranty expired. That's like three different models.
I've never owned a Gigabyte display, but the reviews of that one are pretty good other than the contrast issues causing problems with black uniformity. It has a few other small issues as well, but everything has some kind of issue. I have never seen a "perfect" monitor yet, although I'm sure there are some out there that come really close especially with some of the newer technologies.
My preference would be for the LG but the Gigabyte is also a good option if having uniform black colors that are deep black and not gray isn't a huge issue for you.
Maybe consider going with whichever is less expensive AND you might also want to consider whether either of them has a closer warranty return center than the other in the event you should have a problem. That alone, the convenience of not having to send it back overseas, might be an important consideration.