NW-NDMP Backup to Data Domain VTL or DAS?

Hi

In addition to current existing backup (ddboost based backup). we need to implement also NDMP backup for NAS filer.
According NW admin guide, use of NDMP-DSA or NDMP Tape Server (VTL)  would be technically possible in our environment. 

What would you recommend as better and more useful method to use in together with ddboost?

Thanks