Msc in popular field in less reputed university or not so popular field but in well recognized school
A Master's should demonstrate a broad understanding, which goes beyond Machine Learning / Computer Vision. You need multiple Profs, not just one.
Rankings are subjective, but a well-ranked university is likely better than a low-ranked one.
So, (2) is better than (1), IMO.
That said, these surely aren't your only options: Perhaps look for a leading institute with excellent professors.