Option 2.
The criteria is that ERP is to be used for transactional processing - i.e. running the business. If you're doing analysis on data for reporting - do it in BW, unless the analysed data is required for operations. Even then, think twice about it. BW is designed for multiple source systems and for data analysis.
You might need to write extractors for each local ERP system, but these should be as simple as possible.
Regards
matt