jobs are quite different. While in IBM you will serve the same industry with a few functions (I imagine operations, sales, and analytics) in MBB you will be more a generalist, serving a broad range of industries (e.g. banking, consumer goods, pharma) and functions (e.g. strategy, marketing&sales, digital).
In terms of exit options, within IBM and its few other partners, you would have a good visibility with their internal consulting. However, for any other big companies, MBB are much more appreciated for business positions.