B550A Chipset was only for prebuilt machines. It is essentially B450 with PCIe 4.0 slapped on. It does not have the added IO benefits of proper B550.
However, the MSI B550-A Pro is not using the B550A chipset. The B550-A Pro is regular B550.
Both the B550A-Pro and B550 Tomahawk will perform about the same for the vast majority of uses. The Tomahawk has a slightly better vrm, some flashy lighting, and a couple of other features that Lutfij mentioned. Overall functionality is the same, and system performance will be the same.
I would go with the B550-A Pro since it is a very good board and has all of the features you need without being excessive and adding cost.