Uploading CSV/Excel data, present mapping functionality or download the schema?

With this question assume the users understand CSV/Excel.

I am looking for the most usable approach for importing data (5-15 rows) into an application.

1. 
   
   

   Is it better to let the users download an Excel/CSV template, populate then upload?

   
   

   or

   
   


2. 
   

   Is it better to let the users upload whatever Excel/CSV they have and allow mapping functionality?

   
   

   or

   
   


3. Tell me a better way.

My thoughts are they you usually give the users some-kind of confirmation on what to import, so why not just go ahead with the mapping functionality and kill two birds with one stone?

Answer

You could tell them what columns are expected and have a button to download a blank file for convenience (#1) or let them create / use their own file.

Once the file is uploaded, if the column names don't already match, you could provide the mapping functionality (#2).

An experienced user might already have the file with the right column names and could skip both steps.