I'm a little partial to Asus. From like 20 years ago, if you wanted reliability, you got an Asus, mainly because Gigabyte and MSI hadn't come to their own yet.
Now, ASRock changed all that, with affordable quality and all that...winning some THG awards for a feature set that rivaled the others at a cheaper cost.
My recommendation is totally un-scientific, and not based on any facts mind you. Just a feeling of brand loyalty, warranted or not, that ASRock gave you more for your money, but Asus still reigns...
I will say, from experience, that my Gigabyte mobo from my 2600K build did have issues from time to time...So that's why I won't spend my money on Gigabyte...
MSI... I never tried them, heard good/OK things...
ASRock, again budget focused, still good...
But Asus, and especially ROG, still wins my dollar...totally personal choice...and may not make sense/apply to your situation...
Now Strix is the budget, gamer-y, focused branch of ROG, and not true ROG...
The cheapest true ROG boards are the Maximus/Crosshair HERO boards...the entry level to ROG...
Join me...join the republic...
and for Pete's sake...check out my build...it demands your attention...
If you wanted an actual quantifiable difference, you could say the Asus has two NVMe M.2 slots to the ASRock's one.