Even though all the vendors use basically the same BMCs, Supermicro was up there for me.
Asrock did change their FW recently on all newer boards, newer then my EPC612D8A at least.
The only thing that supermicro locks behind a license is the biosupdate from the ipmi. I think that is called “out of Band update” short oob and requires a oob license key that costs about 20$. The Key is dependent on the BMC Nics Mac address and can easily be forged yourself if you don’t mind.
The html5 ikvm that is included since the X10 generation and the first Aspeed BMCs, does not have the option to add remote usb sticks and iso, you have to do that in a different place in a different way, or you use the older java-ikvm.
Two major features that the supermicro ipmi has over many others is Postcode snooping, so you can see where it is stuck if you don’t get a picture. Though Epyc is a weird platform and someone changed around all the postcodes, so nothing makes sense there.
And the second one is the option to reset / restart the bmc.
You should never need it, but i need it on the Asrack epc since that is a bit buggy sometimes.
That is all i remember. Any specific questions?
Had SM x9, x10 and H11 boards around, as well as the mentioned older Asrack, some Asus Z10 and a hirrible lenovo / ibm thing.