The verdict
If you run an online store and want purchase and browsing behaviour to drive your messages, pick Klaviyo. A connector cannot give you segments, flows and revenue per flow on its own. If you are a small B2B team with no store, pick Zapier. Klaviyo has no deals pipeline or account view and a CRM such as HubSpot fits better, while Zapier will connect your forms, CRM, billing and chat without a developer. Stores with many other tools may end up using both, with Klaviyo for messaging and Zapier for the odd hand-off. Check that Zapier lists the apps you need before you rely on it.