I find anything that doesn't support U2F keys annoying. It doesn't add any friction when the computer just says "push the USB key", since it's a yubikey nano that's always plugged into the computer.

What REALLY annoys me though is places that do support U2F keys, but only one. Last I checked AWS was broken in this regard. And honestly that adds enough friction that I'd rather do experiments on GCP, which doesn't have this bug.

Not that my experiments affect AWS's bottom line. But it does mean that I learn GCP better, and maybe will recommend it in a work context. Not recommend it because MFA, but because I will better be able to say what GCP product can and can't do, than AWS, because of this.