As someone who has built 8+ Ryzen systems using all the major motherboard manufacturers, here is my take on AM4:
ASRock: Good motherboard designs with excellent power delivery at the high end and very reasonable designs for their midrange. Offers more features at a given price point than competitors. Had some very solid designs with first generation Ryzen, particularly the X370 Taichi, which is arguably the best board for the 1st generation Ryzen. Their mid-range boards were also solid performers.
ASUS: Good hardware on their flagships (Crosshair series) with every feature imaginable, but buggy BIOSes. Alas, I had one of the early Crosshair VI Hero boards which self-bricked. Definitely not a good first impression. Avoid their "TUF" series or B350 STRIX boards as they use cheaper components (read: less efficient, more heat on VRMs).
MSI: Cheaps out on components wherever they can, and must have bought a boatload of Onsemi FETs for their power delivery... Their lower end boards get very toasty on the VRMs with 8-core CPUs and long-term reliability is suspect. Seriously, their VRM designs are the worst, and they are beaten by ASRock in value at every price point. Their only saving grace is their memory profiles worked since Day 1 and up to 3600 MT/s in my experience. Even on a $50 B350 board.
Gigabyte: Decent hardware on the high-end and mid-range, but often skimps on the lower end boards. Crippled by what is quite possibly the worst BIOSes for AM4. I still see people running into the Auto XMP bug from time to time... at least they seem to have squared away that 1.55V CPU vcore bug...
VRM comparison of X370/B350/X470 boards:
https://www.hardwareluxx.de/community/f12/pga-am4-mainboard-vrm-liste-1155146.html
Disclaimer: I tend to run my systems at or near 100% load 24/7, so I overemphasize the value of a efficient (read: cool running, longer lasting) VRM.