What is more important for the admission of masters program?
For a purely course-based Masters, in which you do not do research, the research strength of the university obviously won't matter very much.

For a Masters in which you do research and create a thesis, however, the strength of the research group is likely to significantly outweigh the reputation of the school.  This is because the most valuable thing that you can have when applying either for a Ph.D. or an industrial job is a strong recommendation letter from a respected colleague.

If all I know about a student is that they got a Masters from MIT or Berkeley, well, a lot of students get such degrees, and some are excellent while others are worthless outside of the structured environment of the classroom.  On the other hand, if the student comes from Mid-Ranked U with a strong personal recommendation from somebody whose work I know and respect, then they are likely a much better prospect than the unknown from a high-ranked university.