Best of luck for tomorrow - i'd be really greatful if you could let me know the sorts of things they ask. Out of the tow i'm not really sure at this stage, but if in the unlikely event I got offers from both i'd probably go for Bain. They seem to be slightly mre prestigious, plus one of my good friends is starting there next year and has very good things to say about them - he chose them over a BCG offer.
