It depends, there's not really just one answer. The Extreme is EATX and has the sideways cables on the right side, so kinda EATX++ for case size once you allow for cabling. The Formula is above the Hero in the lineup, so Extreme is your choice if you want a bit more than the Hero offers.
If it's all about custom loop, the Hero + the EKWB monoblock lets you create a DIY X670E Formula for the VRM cooling.
You could save a few bucks and go with the top of the line Strix motherboard.
The ROG Strix X670E Gaming Wifi is an excellent choice, you pretty much get everything comparing it to a Maximus board. It has a clear cmos button, a bios flashback button and the LED Q-code read out.
It has two 8-pin cpu power connectors just like the Maximus boards too. 32GB (2x16GB) 6000MHz DDR5 memory would pair nice.
If there are particular features you want, you can check the Tech Specs of any ASUS motherboard.
As an example, here is the motherboard I listed above.