There are a lot of differences between Aurora/RDS and PlanetScale I could talk about, some but I'll point to just one for now: PlanetScale offers Metal databases, which means blazing fast NVMe drives attached directly to the host where Postgres is running. This gives you faster reads and writes than what either Aurora or RDS can achieve with their network-attached block storage. Check out our benchmarks: https://planetscale.com/blog/benchmarking-postgres

Also, the architecture of Aurora is very different from PlanetScale's:

* AWS Aurora uses storage-level replication, rather than traditional Postgres replication. This architecture has the benefit that a change made on an Aurora primary is visible very quickly on the read replicas. * PlanetScale is a "shared nothing" architecture using what I would call traditional methods of data replication, where the primary and the replicas have independent copies of the data. This means that replication lag is a possibility customers must consider, whereas Aurora customers mostly ignore this. * If you set up 3 AWS RDS Postgres instances in separate availability zones and set up replication between them, that would be roughly similar to PlanetScale's architecture.