NICMAR is not a traditional university with traditional courses. Other than engineering, each course contains subjects from a variety of fields. Students at NICMAR are trained to be techno-managers, whereas GATE can place you in an engineering college to pursue an M.Tech, limiting your field to engineering.
If you only want to pursue core engineering aspects and a degree, GATE is the way to go. If you want to broaden your horizons, NICMAR is an excellent choice.
NICMAR also offers decent placement opportunities. In the 2020 placement drive, the average CTC offered was 6 LPA.