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Is AsRock more reilable than Asus?
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Asus has a good reputation for high-end boards, specifically for extreme sub-zero overclocking, but these are in the budget end of the market so I wouldn't expect significant diference in reliability. And also, B550's are way to soon out of the gate and so much changes from board generation to generation it's not really meaningful to make broad statements about reliability.
I think either will get similar software support as B550 is going to support Zen 3 so you can bet they'll get BIOS updates regularly, just as all the AM4 boards have. Other software (drivers) depends more on AMD's chipset drivers which you can always get latest from AMD support site and as well the Ryzenmaster software.
Don't plan on overclocking. Not because of the boards but because Ryzen 3000 just hasn't anything left. AMD's managed to figure out how to squeeze out all the silicon has to give without sacrificing long life. People try to, but doing it yourself makes it way hotter so it needs much better cooling, reduces processor life. For all that you usually get very little gain in multi-thread performance and usually a loss in lightly threaded performance. Whether Zen 3 will be any different is yet to be seen.