If you're a creator or solo founder wanting to build your audience through newsletters and personal communication, choose Kit (ConvertKit). Its tag-based subscriber system offers robust flexibility, while the visual automation builder simplifies the process of managing your emails and landing pages. However, if you value advanced visual email design or only need occasional broadcasts, this may not be the best fit, especially as costs can increase with your subscriber count.
On the other hand, if you’re a developer working on a SaaS app needing to send transactional emails, go with Resend. Its developer-first approach comes with an excellent API and SDK, making it a strong choice for projects where code is a significant component. Just be aware that it's not designed for marketers or those needing sophisticated campaign management features. If you're uncomfortable with technical setups or want a more user-friendly marketing tool, look elsewhere.