Mongodb is more flexible in this regard.
I’m sure there’s other big differences but this is the biggest to my experience with both.
> Amazon DocumentDB implements the Apache 2.0 open source MongoDB 3.6 API by emulating the responses that a MongoDB client expects from a MongoDB server, allowing you to use your existing MongoDB drivers and tools with Amazon DocumentDB
So, is this a "managed MongoDB" or is it a NOSQL AmazonDB that just implements the same API as MongoDB? If the latter, I don't think we can assume this is the same thing as MongoDB, because the internals might be completely different.
Maybe I'll just have to read more about it. Hopefully the internal architecture gets away from DynamoDB-style partitioning.