Mailchimp is where most small shops start, and there is usually no good reason to leave. The builder is friendly, the templates render reliably, and the journey tool covers the flows that earn the most.
The catch is that it is a general-purpose tool. Ecommerce data is available but not native the way it is in Klaviyo, so segmentation takes more setting up and revenue reporting depends on the store integration being wired correctly. That is a job, not a blocker.