If you're a developer looking to implement transactional emails with a solid API, go for Resend. It's built for developers, offering a powerful SDK and strong deliverability, making it highly suitable for SaaS applications. However, if you’re not from a technical background or need extensive campaign management features, this isn't the right choice for you.
On the other hand, if you're running a newsletter-focused business or a media outlet and want to grow your audience, beehiiv is your best option. Its built-in referral tools and monetization options via ads or subscriptions provide a growth-oriented framework. Just keep in mind that it's tailored for media-style newsletters rather than product lifecycle emails, so avoid it if you need straightforward automation or lifecycle email capabilities.