DynamoDB vs MySQL

DynamoDB and MySQL are free.

DynamoDB

Free

AWS key-value and document database that scales without a server to patch.

Pros of DynamoDB

No servers to run
Scales with traffic
Fits the rest of AWS

Cons of DynamoDB

Awkward when you need joins
Easy to get the data model wrong
Tied to AWS

MySQL

Free

The relational database behind a huge share of web apps and WordPress.

Pros of MySQL

Easy to find hosting
Familiar SQL
Free Community edition

Cons of MySQL

Fewer advanced features than Postgres
Oracle steers the project