Amazon Aurora is the best fit for these requirements because it provides a MySQL and PostgreSQL-compatible relational database built for the cloud, that combines the performance and availability of traditional enterprise databases with the simplicity and cost-effectiveness of open source databases. It is specifically designed to offer high throughput, low latency, and fault tolerance with seamless scaling and minimal downtime, which aligns closely with the use case described in the question. Other services like Amazon RDS also support relational databases but do not offer the same level of performance and fault tolerance features as Aurora does for high-performance transactional workloads.