If you are provided with both the choice then ofcourse you should opt for MBA rather than M.COM.
Looking at the future prospects MBA has much wider options than M.COM. If you are interested in higher studies that is M.PHILL and PHD then you can pursue M.COM as a career but if you want to enter corporate sector then MBA is the best career as it is a 2 year course and job opportunities are more than M.COM. Considering other factors like pay scale,growth,exposure MBA has much higher scope than M.COM. But doing MBA is also not easy these days. Today we have a cut throat competition and you need to score good percentile in CAT to get a reputed college. In terms of money pursuing MBA is quite expensive than M.COM. So you need to consider all the pros and cons of both the course and see your interest and decide accordingly.