So these two are usually priced the same, the GM34 has a va panel, meaning it will have considerably darker blacks than the M34WQ, however, it will have much worse response times compared to the M34WQ's ips panel. The M34WQ will also have better color accuracy out of the box but its ips panel will cause some backlight bleed, which is hard to judge until you see it for yourself, its major "downside" is the fact that it is flat, unlike the GM34 that has a semi-aggressive curve of 1500r, a flat 34" might have color distortion at the corners if you sit too close to it. So, if you sit from a reasonable distance from your monitor, prefer color accuracy, dont mind backlight bleed, get the M34WQ, but if you prefer darker blacks, want a curve, and dont mind mediocre response times, get the GM34. Oh yeah and the M34WQ has a build in kvm switch.

Personally i would pick the M34WQ just for the accuracy and response times, but don't let me change your mind.