I think hardware keys are the best option for passkeys, because they have a separate (physical) user interface compared to software-based keys. This makes it easier to understand the login process. You physically interact with the hardware key to confirm that you want to log in. And you can use your key for many different accounts.

The downside is of course that hardware keys are typically not cheap and you should also buy a backup key. Another unnecessary downside is that certain companies like Microsoft require the use of resident keys, which take up storage space on the hardware key. The better alternative is non-resident keys, of which you can have an infinite number on your key.