Choose Localstack if you are a developer looking to test AWS cloud applications locally without incurring cloud costs. It provides instant feedback for code validation, which is particularly useful for developing and debugging cloud-based solutions. However, if you require a full cloud environment or prefer an open-source solution, Localstack might not be the right choice.
Opt for Railway if you value a hassle-free deployment experience, particularly as a solo developer or indie hacker. Its Git-push simplicity allows you to focus on coding rather than managing infrastructure, making it ideal for projects where ease of use is a priority. Just keep in mind that after the trial period, costs can escalate and there's no permanent free tier, which may not suit everyone.