Hello student M. Com or CA and MSc in computer science are completely different courses they are not linked with each other. You need to decide yourself on the basis of your interest, eligibility and academic performance. Among all three courses you've mentioned CA is one of the most demanded professional course.

After graduation you can directly take admission in Chartered Accountant intermediate. You need not to appear and qualify foundation exam of CA.

Feel free to comment if you've any doubt

Good luck