We haven't done any builds in that budget range so would be hard pressed to make a recommendation from personal experience. However ....
Both have M.2 Socket 3 support, Giga supports M.2 Socket 1, Asus no.
Giga has SATA EXpress
Giga uses ALC 1150, Asus uses licensed version of ALC 1150
Giga is smaller
Asus has a current rebate for $30 on newegg
Looking at newegg reviews, 50% of Asus board owners gave it a extremely negative 1 egg rating. Although 12 reviews hardly constitutes a statistically valid sampling size, that high a number has got to cause concern.
Looking at the Giga 50% of board owners gave it 5 eggs and just 7% 1 egg. Again, the sampling size is very small at 14, so statistically, potential accuracy is low. But even if sampling error is as high as + or - 15%, it's no where near enough to make it close.
Looking at overall RMA rates for the two companies over last two sampling periods, ... Asus has averaged 1.93% and Giga 1.91% ... in other words "no statistical relevance". But overall rates are not really a good way to judge a board, when introducing a new model or model series, RMA rates tend to be high (i.e. much of MSI M series), Though I would consider any board model w/ a return rate above 2% worth looking into ... I wouldn't necessarily exclude it. Also, if a board model isn't listed, that doesn't mean that it must be good, it may mean that it just didn't sell enough to be reported due to low sample size making the percentages statistically unreliable.
These are boards I'd wanna take a hard look at before buying:
6,64% MSI Z170A Gaming Pro
5,17% MSI Z170A Gaming M5
5,00% ASUS Maximus VIII Hero
4,76% MSI Z170A Gaming M3
4,29% ASUS Z170-Deluxe
2,88% ASUS Z170-A
2,84% Gigabyte GA-Z170XP-SLI
2,31% ASUS Z170 PRO GAMING
No B series Motherboards made the list as sales numbers didn't qualify
So when all is considered, I like the Giga better ... while the $30 rebate makes the Asus very attractive cost wise, when 50% of owners are unhappy with their purchase, it's just to scary. I'd want to invest more time before making a decision if possible ... or perhaps look at other options. In short, I'd "punt the ball" and make a decision later
. But if ya made me pick one, today, it would be the Giga.