No real opinions on the actual boards, but I like using Skinflint to do any comparisons as they've done so much of grunt work:
https://skinflint.co.uk/?cmp=1845608...32&cmp=2111702
The Gigabyte looks like worst spec'ed of the three although it is the only one which mentioned HDMI 2.0b.
The ASRock has ECC support (mostly noteworthy), and the best USB port selection. As DanceswithUnix already mentioned it has two M.2 slots although the 2nd one is SATA only.