Came here to comment this, there's a ton of awesome stuff around Postgres that using RDS makes impossible. Kinda stinks, but I don't have the time/expertise to manage a Postgres Instance on EC2.
If you have kubernetes experience, running a cluster using a pre-built helm chart (like pgo) takes away a ton of the pain by bundling needed services together and giving you easy upgrade paths, high availability, backups, etc.
If the extension availability is the main concern, I'd recommend the open source StackGres [1] operator, which has, possibly, the largest Postgres extension catalog [2] available.