Among the three mentioned universities, Jadavpur University is the best to pursue BSc in mathematics Honours without any doubt. The classes are assured regularly and rigorous for those who desire to have a future in mathematics; there should be no doubt in selecting JU. 

Comparison: (Winning Institution - Jadavpur University)

• St. Xaviers became a university recently. A BSc degree from JU holds more value than a bachelor’s degree from St. Xaviers. 
• Jadavpur University was ranked 196th in Asia by The World University Ranking 2020.
• The faculty at JU is top-notch. The syllabus adopted by JU is of advantage if you want to pursue higher studies after your degree. You will have better exposure at Jadavpur through regular seminars. Attending seminars delivered by guest faculty from distinguished National institutes, and your seniors pursuing masters and Ph.D. will make an immense difference.
• If you are choosing St. Xaviers because of the campus, you should visit the Jadavpur University campus. 
• The classes are regular, and JU follows a rigorous pedagogy. The political environment people talk about is quite exaggerated. If you don't get involved in campus politics, it is never going to bother you. 

Jadavpur University contributes much more than just a degree that gives you quality education, which is not restricted to classroom learning. They make sure the students turn into the person they can be and gives them the confidence that no other college in Kolkata does.