I've just finished my XII and want to know if I should do CA with a regular college or should I do B.Com and try to go to IIM for MBA?

If you do CA, make sure you have B.Com degree. That will have you a push in market. But if accounting is not your Forte then don't even think about CA. Go for MBA. For getting into IIM, you need to score high in CA. Exams. Before attempting go for coaching for atleast 1 and a half years.