Go to:
http://www.newegg.com
and then paste this on the end of the url
/Product/Productcompare.aspx?Submit=ENE&N=-1&IsNodeId=1&Description=Asrock%20Z170%20Pro4s&bop=And&CompareItemList=-1|13-130-874^13-130-874%2C13-130-867^13-130-867%2C13-157-635^13-157-635%2C13-157-636^13-157-636&percm=13-157-636%3A%24%24%24%24%24%24%24
Here's what we get ...
-Both the MSIs come with ALC 1150 ...both ASrock come with ALC892... a huge drop in audio quality.
-The Asrock boards support higher memory speeds, will it matter ? (3866 vs 3600) Not if ya not planning on buying 3866.
-Only the MSI Gaming Z170A supports SLI 3 x PCIe 3.0 x16 slots (support x16/x0/x4, x8/x8/x4 modes)
That does it for me ...
1. The cheap ALC 892 audio solution just kills both AsRock boards as suitable gaming choices
2. No possible SLI option kills both ASRock and 1 ouytta the 2 MSI boards cutting you off from the option to extend system life by 18-24 months by buying a 2nd card someday.
MSI Gaming Z170A would be my choice among those. However, I am concerned about the high % of negative reviews on this board ... granted the small sampling makes it hard to say the results are statistically valid, and not as high as many popular Asus boards, but it's enough to make me shy away.
So while among your choices, the MSI Gaming 5 stands out features wise above the other 3, The Gaming 3 from Gigabyte has much more happy owners, ALC 1150, gorgeous looks and a great price and supports SLI making it an easy choice.
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128837