For me -- I favor boards that have extractable BIOS chips. They have been called PLCC chips. You can find outfits who will flash the chip with the appropriate BIOS version in your order request, and they will even give you a discount for turning in your old one for re-use.
So it just occurred to me that I didn't even think about that preference when I picked my Z170 board. I haven't even looked for it. But I think I see the PLCC chip sitting just above PCIE-x16-2 near the forward latch. Correct me if I'm wrong:
My Sabertooth Z170 S
It should be obvious that there's a history here or there of BIOS revisions which bork the existing BIOS or make the system unresponsive and unbootable. So the way to avoid the RMA hassle under warranty is simply ordering a PLCC chip with the BIOS you want. One web-accessible store-front was BIOSMan, but somehow he disappeared for an extended period of time -- posting notice or advice on his web-page. ASUS itself, as far as I knew some few years ago, offers replacement chips with custom-order versions. For the $10 to $30 expense and whatever it is now, it's good insurance and could even be a lifesaver. Depends on whether you can suffer the downtime for order-fulfillment in your choice to order in advance or order in the aftermath of panic.