In terms of quality and durability they're pretty much identical.
In terms of function: You'll get the benefit of more PCie gen 4 lanes with the X570 chipset. If you have a lot of PCIe gen 4 devices you need to run (NVME drives and PCIe slot peripherals) you'll have greater flexibility with the X570.
B550 chipsets have quite enough to handle any normal useage though: one gen 4 NVME with 4 full lanes for the system and one gen 4 x 16 lane GPU slot. The B550 board even has slots for one or two PCIe gen 3 NVME's, which you'll hardly notice as any different from the gen 4 NVME . Or, if you don't mind stealing lanes from the GPU, you could use them for gen 4 NVME's.
Both have very capable VRM's that will easily handle even a 5950X processor. But if you're considering overclocking one, especially with sub-ambient cooling, then the X570's will prove marginaly better. Otherwise either one will run cool and quite under stock settings or overclocked.