I'd pick Bain AC. I question McKinsey's commitment to their Business Technology practice (BTO and subsequent incarnation)... they have a hard time differentiating from the likes of Accenture / Deloitte / EY while still wanting to charge higher rates. Perhaps this explains why it's been on and off for the last 10-15 years.

But the more important question is what you want to do in your career? This should be an important driver in your decision.