Our recommended best practice is to create a non-human integration user for this connection (i.e., peopleaiintegration@domain.com)
For any of the three options presented, the integration user must be at the top of the Role Hierarchy in order to have the full visibility needed to pull from and push to Salesforce.
For additional details on what People.ai will use for each Salesforce Object or field, please refer to: Object Permissions or Field Permissions, respectively.