Hello,
The services and reports generally have different data.
The services will show you the actual structure and setup of your account. You will be able to easily see which ad groups are in which campaigns, which ads are in which ad groups, etc. You will be able to see a complete list of all ad groups, ads, etc., whether they're serving or not. If you want structural information about how your account is set up, then you should use services.
Reports have statistical information about how your campaigns, ad groups, etc. are performing. You cannot get information like impressions, clicks, etc. from the services. For this information, you must use reports. However, the reports don't have detailed information about the structure of your account.
I hope this clears up the difference!
Regards,
Mike, AdWords API Team