They are also known as MBB. Who are the CEOs of the three main consulting firms (McKinsey, Bain, BCG) and the big 4 (EY, KPMG, PwC, Deloitte)? When we talk about the big 4 and the top 3 firms, we are talking about the highest level of accounting and consulting firms. The Big 4 are the largest firms in the entire world. They have the experience and resources to address any of their customers' needs.
The 3 best, also known as MBB, aren't that big, but are generally considered to be the best.