You can't chose between the two in Outsystems it handles it automatically, also you can only ever have one clustered index in a database table. Looking at the created tables in SQL Management studio below is how it works
When an auto increment fiend is created that field is set as the primary key which is clustered. Using the default pattern for creating entities this will be the ID field unless you manually change it. As an Auto Increment field it is by definition unique.
If you are using a multi tenant database a second non clustered index is automatically created for the tenant_id field and any other index you create will automatically have the tenant_id field added to it.