Any guidance on when to use a Shared channel vs. a Guest account?

This is an excellent question. While I don't have much experience with Shared Channels yet, I have leveraged Guest Accounts for clients to satisfy security requirements. Specifically, with guest accounts, the inviting Microsoft Tenant can enforce that guests have to log in and authenticate their identity using multi-factor authentication. Further, the inviting Microsoft Tenant can even specify the MFA type (either passcode received via email or SMS-based passcode). This might be one factor to consider when determining between either option. I am curious to hear what others have experienced in this regard.

Update: One other major consideration is that with Guest accounts, the guest is exposed in other Microsoft 365 Apps such as SharePoint Online whereas with Shared Channels, the guest will only have isolated access to channels they are invited to.