I have a few friends from University of Allahabad and according to them, the faculty at Allahabad University is amazing. Moreover, the Maths department is the biggest department in Allahabad University. The teachers are well-experienced and cooperative.
The faculty at Allahabad University is not only famous for Maths but also for Chemistry. And due to this reason, every year you get to see at least 2 to 3 students clear in research exams and further get selected in IITs for research.
You can consider University of Allahabad as a valid option for your B.Sc in Mathematics.
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)
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.
To do a BSc major or honors in Mathematics from IGNOU, you will have to complete Elective courses worth 40 credits in Mathematics in the span of three years. Out of these 40 credits 28 credits, i.e. MTE 01, 02, 04, and 09 are compulsory. You can select the remaining credits from other papers.