Both the universities, GIM and NMIMS are reputed in the field of Management education. But since you don't have NMIMS Mumbai as an option, you might give it a second thought.
When it comes to NMIMS Bangalore, GIM is a much older player in the field of PGDM. Even if we see the rankings, GIM is considered in the top 20 to 30 including IIM in the list. They have experienced faculty, very decent placement records, and a very strong alumni base.
So I would suggest not running after an umbrella institute under the NMIMS brand name and rather going for GIM.