Since you are in a .NET environment; it would possibly be easier to work with SQL Server.
On the other hand your question can't be answered that easily. It depends on how your data is structured or how you planning on structuring it.
SQL Server being a relational database, and DynamoDB being a document based database, both have fundamental differences in how you store and retrieve your data, so this needs to be a consideration in your design.
I'd also like to mention that SQL Server is a server; as to DynamoDB which is a service; replication, scaling, backup all come built in and since it's a managed service, it usually doesn't need your consideration to set this up, it'll just work; costs on DynamoDB might also be something to consider; you pay as you go might be cheap to start with, but might end up being expensive if your application scales; properly defining your reads and writes is a must to keep that in control.