When it comes to size, breadth, and reach, McKinsey has always been the market leader. As the youngest of the three firms, Bain is the group's start-up and its lack of experience is offset by taking risks and differentiating itself in the market. When I started working as a consultant at Accenture, it was prestigious to work at MBB and Accenture was a bad word. But when I moved to McKinsey & Co 12 years later, things had changed.
However, BCG has become increasingly active in engaging its alumni network, and my subjective impression (as a former student of McK and BCG) is that they have managed to close part of the gap with McKinsey. Whether the customer is a traditional company that has not used digital technology before or a company that is undergoing a digital transformation, McKinsey Digital, a horizontal practice group that provides services to all vertical sectors of the industry, offers solutions. It's best for an aspiring consultant with a law, medical, or other advanced degree to knock on McKinsey's doors first. Parthenon (the leading education firm) recognizes that hiring McKinsey is the surest bet to ensure consistent and high-quality work.
Overall, Bain seems to be well-versed in the work-life balance of its employees, but its private equity firm arguably works more hours than any other consulting group. The McKinsey Knowledge Network consists of 2000 knowledge professionals who work in the company's knowledge centers. According to some industry insiders, McKinsey alumni are believed to have a more prominent position in the business world than those at BCG or Bain in any proposed future work. In addition, McKinsey consultants are more likely than those from the other two firms to be part of the office staff of client organizations around the world. So, while any competitive presentation McK is invited to also has BCG as the launcher (and vice versa), Bain is not always present. In terms of exits, a large proportion of McKinsey and BCG consultants opt for strategy director positions, while Bain consultants seem to be disproportionately biased towards entrepreneurship or private equity.
In addition, working at McKinsey fosters strong cohesion and a sense of belonging, which are usually maintained after leaving McKinsey. At the other extreme, Bain has a more pleasant office environment, which one writer describes as “fraternity”. McKinsey has the largest workforce (8000 consultants versus 4.5 BCG and 3000 Bain), hence the largest alumni network. At Bain, consultants are more likely to work in a single office, although they may have the opportunity to work abroad in a client's office. When it comes down to it, there is no definitive answer as to which consulting firm is better: Bain or McKinsey. Each firm has its own strengths and weaknesses that make it suitable for different types of projects and clients.
Ultimately, it comes down to personal preference and what type of environment you feel most comfortable working in.