IBM DataStage vs BO Data Services SAP

Hi Gurus:

We are in the process of choosing ETL tool and now we are looking at 2 options, DataStage and BO Data Services.

I read the datastage document, it seems it also has the ability to extract the BW data source, idoc, etc.

So would anyone give me some idea about what is the advantage of datastage compare to DS, if SAP is the main data source/target?

Thanks a lot.

Best regards,

S Narayan