Which are best college to take degree in Mathematics ?

The best college for Mathematics is CMI Chennai. The system at CMI is pretty minimalistic.

• Attendance is not recorded, although the small size of the class usually ensures that the prof gets to know the regular absentees.
• There's no uniform system of marking or even any set course structure, which is entirely in the hands of the professor taking the course.
• Apart from the core courses, you can attend any course of your choice which is being taken at CMI. For example, a BSc 1st year student can even take a course of an MSc 1st year student (and vice versa too) Of course, there's the trouble of clashing timings, but it can be easily adjusted. Basically, there's the matter of talking with the professors who are, in general, very supportive and most importantly, approachable.
• There's a lot of free time available. Saturday and Sunday are free.
• The campus is pretty small and quite green. Small enough that you can walk go from one corner to the other within 5-7 minutes. With the mess right inside the hostel, the mess is just 10 steps away from room. So, get up at 8:45, take a quick bath, have an even quicker snack, and you'll find it's still just 9:05, enough time to easily go to class.
• Another really nice thing about CMI is that the library and Computer Lab are both 24x7 open. You can often go to the library pick any topic of my choice, and just pick any book that seems exciting.
• There is a daily shuttle from CMI to IMSc, which goes like 5-6 times a day. It's not only useful for going to IMSc to attend the guest lectures there, but the nice thing about it is that IMSc is pretty close to IIT-M. (Not to mention that it is at the heart of the city, and near the beach, so you can roam around, shop, or go the beach)
• Finally, for recreation, there's a common room with Tata Sky TV and a Gym. There's a Table Tennis table, and a makeshift badminton court. There's a proper volleyball court, and half a basketball court, I guess there's football ground coming up soon too.
  
• To top it all of, a monthly stipend of Rs 5000/- is paid by CMI to every student.