now I am studying 12th ,MPC .So which group is best to select for writing IAS EXAM
There's no such thing as best degree for IAS.You need to be a graduate to be eligible to appear for UPSC IAS exam.So, it depends on your present interest, you can pursue B.tech after passing your 12th, you can also pursue any other 3 year degree.The syllabus for IAS is not entirely same as any other degree syllabus.So it doesn't matter which course you choose.
But make sure that you pursue what interests you.
I hope this is helpful to you.
don't waste ur time by going through b.tech courses. complete a degree related to social sciences which will be helpful to improve your knowledge.