Both of them are equally great, but MMS has seen slightly better edge becuase it terms itself as degree course as Agaunst PGDM which termed as diploma course.
MbA or MMS candidates have good advantage for Phd and Fellowship programmes where some colleges prefer MBa students against PGDM.

However, its notable that PGDM has better learning updated industrial curriculum as against outdated curriculum for MBA.

So both have thier own pros and cons.