You are definitely right in thinking that the data overlaps. Basically, it just comes down to the level of granularity that you want to show starting at campaign > ad group > keyword / targetexpressions > search term > productad / asin.
We believe a good place to start for report building is with the sellermonthmetric and campaignmetric tables. sellermonthmetric contains the campaignmetric data rolled up at the month level for each ad type - this makes it extremely easy to use for reporting dashboards as you don't have to implement date ranges or aggregations. campaignmetric will give you data for each campaign, of which often represent the objectives that an ad manager is trying to achieve.
Lastly, it may be useful to show data from the productadmetric table as this will include performance at the ASIN/SKU level. Amazon does not provide the product names for each ASIN, but we are working on solving this with our MWS build. In the meantime, you can use the reference list exported from Seller Central or Vendor Central to populate the ASIN names via a blend on ASIN.