Model B450 or B550
Model B450 or B550
B550 is compatible exclusively with upcoming Ryzen 4000-series CPUs from the Ryzen 3000-series lineup. The Ryzen 2000-series models (such as 2600X, 2700X) are not supported. Based on current information, manufacturers seem unlikely to extend support for 2000-series and earlier chips.
The Gigabyte B550M AORUS PRO offers a more affordable option compared to the MSI B550-A PRO, especially since both are compatible with ATX or Micro-ATX setups.
They're both okay. I'd still choose the pro if the price gap isn't too big, otherwise it'd be a great deal.
The A Pro stands out more. Skip the extra features like debug LEDs and opt for the B550 Aorus Elite if you're okay with it. It offers top VRM performance, though it misses some A Pro perks such as debug LEDs and a built-in Type-C port. Alternatively, consider the Prime B550-Plus. The B550M Aorus Pro can overheat when using a 3900X, and the 3950X won't work well without proper cooling on the VRMs—especially since the plastic insulator makes airflow difficult.