Use Einstein Activity Capture when you want reps’ email and calendar to reach Salesforce records without anyone clicking Log. Pick Salesforce Inbox only when reps also need email tracking, Send Later and meeting availability inside Outlook or Gmail, because an Inbox license already includes Einstein Activity Capture.
So the real question in Salesforce Inbox vs Einstein Activity Capture is not which one wins. It is whether Standard capture is enough, or whether your reps need the paid email tools on top. I checked both setup pages and the licenses in a Winter ’27 org. You will learn what each does, where its data lives and which to turn on first.