The answer to your question lies in what objects are in your current reports. Each project is different. If you have dynamic straight tables that can span multiple pages, then you need to use the Excel template and come up with a logical page break strategy. If you have charts that are a fixed size, you can use Word or Powerpoint. All of these templates will enable you to export as a PDF when creating your report.
When I first started using NPrinting, I watched the beginning and advanced videos provided by Qlik. Frank Savino does an excellent job of showing how to get a project started and using each of the available templates.
As I am sure many on here will attest, competency comes from trial and error.