I would always suggest an MBA.

Choosing between these two degrees depends upon why you want to pursue either of these degrees in first place. The degree Master of Business Administration is not the same as MIM. The MBA is a general broad degree covering a wide variety of business issues and training students for careers in managing any area of business.
The MIM is a degree that concentrates study in a specific field, such as finance, accounting, taxation etc and trains students for careers in high level staff positions often involving research. So MIM degree would provide you focused and concentrated information and MBA would be having wider subject range and you would study subjects regarding management also apart from accountancy or tax.