Well that's a nice dilemma - both look pretty good.
Predator has larger screen (31 vs 27 inch) and VA panel technology (some would regard as superior to TN panel technology of the ROG).
ROG has faster grey to grey response time (1 ms vs Predator 4 ms, though some are cautious about the GTG metric).
Prices fairly similar.
You should probably try to sit down at both in a shop if possible and try them out - see if you have a strong personal response re the panel technology (some reviewers complain a lot about TN on some models, colour and image quality from an angle issues).
Based on specs alone I would be leaning to the Asus ROG (I would be happy with the TN, esp. for my gaming setup, to get the faster response time).
But I think it's a pretty difficult call, and others would no doubt have strongly divergent opinions.