Hello! In my opinion, both phones would be great options for you. I have an Honor 8 myself, so I know the 6X would be a worthwhile alternative. Honor phones last long - I've had mine for almost eleven months now and have encountered minimal signs of age. Of course, I've heard good things about the G5 Plus as well.
The Honor 6X does have a bigger screen (G5 Plus is 5.2") and a bigger battery, however. What are you looking for most in a phone? That may help you narrow down your search.