If you don't have a previous generation Ryzen CPU, then you'll need a board that is either Ryzen 3000 ready out of the box; or one that has a flashback feature, so the board can be flashed with the latest BIOS without the need for anything other than a PSU.
MSI's MAX range come Ryzen 3000 ready, so an ideal choice. They are the only boards that come Ryzen 3000 ready AFAIK. Any other B450/X470 board will require updated BIOS. MSI's non MAX versions of those boards; some have a flashback feature, so can be updated to support Ryzen 3000. Many of those will eventually receive an updated MAX version though.
Motherboards from other manufacturers will either need a similar flashback feature, or the board would need to be flashed with latest BIOS prior to shipping. If you were looking at a Gigabyte Aorus Elite or Pro, for example; then you'd need that to be flashed before shipping. Sadly, this is a service that OcUK don't offer. Buying from OcUK, makes it trickier to look at anything other than an MSI board for a new Ryzen 3000 build.
Having said all of the above; the MSI Tomahawk is a good board. Tomahawk MAX should also be, as it's just an updated version. I've been considering that myself along with the Mortar MAX (yet to be released). I was also looking at one of the Gigabyte Aorus boards as well prior to considering the MSI boards, but with no flashback feature, I'd have to look at getting that from somewhere that offers a BIOS flash before shipping service. Some places offer this service, some don't.