The verdict
If you run a SaaS product and your emails should follow sign-ups, activation and cancellation, I'd pick Loops. It also removes the need for a second system that sends password resets and receipts.
If you are a services business, a B2B company without product events to send, or a team that wants SMS and a simple CRM, I'd pick Brevo.
Be honest about data. Loops is only as good as the events your product sends, so plan some engineering time. Brevo asks less of engineers. Neither suits cold one-to-one sales outreach, where Instantly, Lemlist or Smartlead fit better.