Both colleges are great options for studying statistics.
Presidency University has a glorious history and the department of Statistics is one of the best departments. The university has great alumni which makes it score higher in terms of ‘Heritage’. One of the most famous names among them is P.C. Mahalanobis. There are dedicated faculty members like Prof. BR and Prof. PD, who is an alumnus himself.
One of my friends has Statistics as his electives but he never got the chance to be taught by these reputed faculty members. Students are highly dedicated and excels in their respective university exams.
Graduates from this college pursued post-graduate studies from reputed universities like ISI, CMI, IMSc, etc. If you have Honours in Statistics with Mathematics and Economics, then it will be a great combination.
In terms of environment, you will get a sense of freedom at Presidency and a change to form a opinion on various aspects of life. However, St. Xavier’s College is also good but it is very strict and you will get a feel of school there. It is known for its discipline while Presidency University is know for its creativity.