stevenjemint :
B450, its the newer of the two and has some better support for OCing
It's not really the chipset (B450) that allows better overclocking the later motherboards, it's the VRM designs. In particular (in that lineup) Asrock B450 Pro4, with a truely solid VRM, is a good choice since it is lower cost. Otherwise I'd go with the B350 Pro Carbon.
And another thing in favor of the Asrock...but I totally wouldn't base a buy decision on this alone. Ryzen 3000 chips will support PCIe gen 4. While none of these boards, predating Ryzen 3000, are marketed and spec'ed to support PCIE gen 4, if the device is within 6 inches of the CPU (which provides the lanes) it MIGHT still work. The only device that would make that worth it is the NVME and...