Asus H170 Pro Gaming VS. Gigabyte GA-Z170XP-SLI ?

Personally I feel Asus is a better brand, but I would go for the Gigabyte one, as Z170 is better than H170 (for better SLI support and Overclocking ability in the future). But do go for a K series unlocked Processor (i5-6600K preferably).

ASUS has Q-LED (CPU, DRAM, VGA, Boot Device LED) is one very handy feature, as the respective LED lights up incase of any problem with your System and also has an additional Display Port.