If you're a solo creator or founder focused on building your audience, Kit (ConvertKit) is your best option. Its flexible tag-based system for subscribers allows for tailored marketing, and the visual automation builder is user-friendly for crafting engaging workflows. However, if you prioritize creative and visually stunning email designs or only require occasional broadcasts, you might find Kit limiting.
On the other hand, if you're a developer working on a SaaS application who needs a robust way to send transactional emails, Resend is the better choice. Its API and component-based templates using React Email make it ideal for developers looking for flexibility and strong deliverability. Just be aware that it’s not designed for marketing campaigns and may require more technical know-how, which could be a drawback for those needing a straightforward marketing tool.