Help me choose between offers

Any is fine, would pick S& personally

All of those are solid places. I’d pick the one where you fit best and it sounds like that’s S&

I would say S&. You already like the peopleb and pay being higher is good.

Something else is that Deloitte and EY-P have been going through re-orgs that seem to have diluted the brand. Go on some other threads here or on fishbowl to read about it. Some parts may be overblown but it seems like S& has done of a good job of truly being the strategy arm of PwC and keeping the brand separate. That's important for your career as you don't want your brand to be diluted in the future just because management decided a re-org would streamline product offerings.

I would personally choose Strategy&, however the others aren't bad options though.

All good for internship and will help craft story for MBB. None will secure it so wouldn't make that part of your decision making 

Do they differ by location?

Assuming all else equal, I would go with fit since it will help you perform better during your internship.