Both of Christ and St Xaviers are established and famous colleges for Bachelors degree. However St Xaviers Kolkata, has better faculty and academic outlook, when it comes to Bachelor of Science . CHRIST University is primarily famous for its flagship B.Com and Finance/Economics/Commerce Degrees.

Although I would like to add a point, if you prefer going for a Government Job, Masters degree or MBA post B.Sc. prefer St. Xaviers, Kolkata whereas if you plan for Placements post BSc., I believe CHRIST University and Bangalore itself will provide better opportunities in that regard. Do choose wisely.