It really depends. Coreboot is open source and you can review the code, it's also much lighter (though fewer things can be tweaked), vs AMI which we don't know/can't check what it contains.

For me, wanting as much open source in the stack as possible, it gives me peace of mind, but it really depends on the individual.

All I can really suggest, is to take a look at the Coreboot site[0] and see if it sounds like something you'd want.

[0]https://www.coreboot.org/