I use 1Password (and the browser extension) for all my passwords, but I still choose "Sign-in with Google" when that's an option.

The "Sign-in with Google" button is makes it much quicker to create an account and slightly quicker to log in.

Also, I can rely on my Google 2FA rather than setting up and filling in a different TOTP for each site. Something like U2F or WebAuthn would make the filling-in part more convenient, but even sites that offer 2FA usually don't offer those. (And many sites don't even offer 2FA.)

Using 1Password's 2FA feature would make TOTP more convenient, but I'm a little nervous about putting 2FA in 1Password. This might be overly-conservative thinking, though.