The answer to this for me anyway depends entirely on the size of the solution, what the rest of the stack looks like, how many users, what is my support contract like etc etc, do I have to collaborate with other engineers or is it just me? Similarly, if you already have a bunch of ops guys managing some RDS stuff, it might make sense to just take advantage. RDS also comes with a ton of features a simple compose stack won't, especially around redundancy and disaster recovery.

I don't think there's a good one size fits all answer to whether hosting in Compose or RDS is right for you or a given project.