The Event Monitoring Log is the best feature to use to see when a user last logged in to Salesforce if real-time notification is not required. The Event Monitoring Log provides detailed information about various events that occur in the org, such as logins, API calls, report exports, etc. The developer can query the LoginEvent object to get the timestamp, username, and other details of the login events. The Calendar Events, Asynchronous Data Capture Events, and Developer Log are not relevant for this scenario, as they do not capture the login information of the users. Reference: [Event Monitoring], [LoginEvent]