I need a AM4 motherboard but struggling to find the right brand
It's curious, but if looking at it from a 'brand' perspective and looking at it broadly (which is probably unfair of course) you can say some brands are better depending on the generation chipset they're using.
For instance: MSI you have to be very careful which board you're looking at in their X570 lineup, while their B450 line was strong, with quite a number of particularly good boards. And both Asus and Gigabyte misfired with most of their B450 boards while hitting it beautifully with their X570 lineup.
And B350 (mostly out of consideration for current purchase, but still widely available) are pretty weak across the board mainly because of the the pitiful heatsinks they used on the FET's with weak 4 phase VRM's. Even an un-overclocked 1700 on many of those boards make for toasty hot VRM operating temperatures when Folding@Home.
In most every instance this is not to say they won't perform at least adequately well, but when you look at what you're getting for the money compared to the competition you can find it shows.