Among the ASRock, Asus, Gigabyte, and Msi AM4 motherboards available in the market today,
A320-chipset motherboards:
- does not support overclocking the Ryzen CPU
- are mATX form factor (with the exception of a Gigabyte model, GA-A320-DS3, which is ATX)
- does not support SLI
- does not support CrossFire (with the exception of GA-A320-DS3 mentioned above)
- only have 2x RAM slots (with the exception of ASRock A320M Pro4 and Msi A320M Bazooka, which hav 4x)
- have only 4x SATA ports
B350-chipset motherboards:
- supports overclocking the Ryzen CPU
- power phases range from 6 to 9: Msi at 6, Gigabyte at 7, Asus at 6 with a model (B350-F) at 8, and ASRock at 9 with a model (AB350M-HDV) at 7
- 15 motherboards are mATX, and 12 motherboards are ATX form factors (most mATX are Asus and Gigabyte; most ATX are Msi)
- 7 motherboards only have 2x RAM slots, the rest have 4x RAM slots
- none support SLI
- 7 to 18 motherboards support 2-Way CrossFire (with the 11 mobos depending on PCIe bandwidth usage)
- 10 motherboards have 6x SATA ports, 17 motherboards only have 4x
X370-chipset motherboards:
- supports overclocking the Ryzen CPU
- power phases range from 6 to 16: Msi at 10, Gigabyte has one model at 7 (Gaming K5) and the rest at 10, Asus has one model at 6 (X370-A) while some are 10 and 12, ASRock has three models at 12 (K4, Killer SLI and Killer SLI/ac) and two models at 16 (Taichi and Prof. Gaming)
- all motherboards are ATX form factors
- all motherboards have 4x RAM slots
- most support 2-Way SLI (with the exception of two Gigabyte models, GA-AX370-GAMING and GA-AX370-GAMING K3, and an Asus model, X370-A, due to the 2nd PCIe x16 slot's max. speed)
- 11 motherboards have 6x SATA ports, 7 motherboards have 8x SATA ports, and 2 motherboards have 10x SATA ports
If you are looking at OC'ing the Ryzen CPU and getting a B350-chipset motherboard, consider getting the ones with higher power phases (such as the ASRock Fatal1ty AB350 Gaming K4).