for example which is better in terms of futute employment-msc in finance from top 50 school of MBA with finance concentation from only an accredited school?

It depends on the person's goals. Compare the average salaries. However, they cannot be compared directly very easily. Most MSc in finance programmes are pre-experience, so someone is either qualified for the MBA or for the MSc bit not both. However, the salary is generally higher after those MSc programmes than for MBAs at unranked but accredited schools: http://rankings.ft.com/businessschoolrankings/masters-in-finance-pre-experience-2012