Booz Allen Hamilton or Roland Berger?

From a pure strat perspective, I'd go with RB. Huge caveat however, they are both Tier 2 and with significant geographical differences. Ultimately, I doubt it'd matter much so chose based on local strength in your area of predilection, and based on the people you meet.

Another thing to keep in mind is the value of staying in current company (strengthen existing network) vs. adding another company's (developing new one + getting access to that new company's resources). No wrong answer, just make sure to include in your calculus

I would tend to agree with Guennael that RB will generally offer better "strategy" opportunities. However, their geographical presences vary significantly, with BAH being more well known in the US. Therefore, if your end target is a top US MBA, it might actually be better to stay at BAH.