If you're a developer working on a SaaS application and need reliable transactional email functionality, go with Resend. Its developer-first API, excellent SDK, and strong deliverability defaults make it ideal for embedding email services within your applications. However, if you're looking for a more marketing-oriented tool with advanced campaign management features, you should avoid it, as it caters more to technical users.
On the other hand, if you're a solo creator or a small business looking to manage and schedule social media posts easily, Buffer is the better choice. Its user-friendly interface and support for major social platforms make it accessible, especially for those new to social media management. Just be aware that if you need advanced analytics or plan to manage many channels concurrently on a budget, Buffer might not meet your needs due to its basic analytics and potentially escalating costs with per-channel pricing.