What are the advantages of BCG in comparison with Mck? I've found only one: long history of innovation (learning curve, BCG matrix, segmentation, time-based competition). Are there any more?

There are lots of differences and people who have the choice between the two can go either way - though in my experience a higher proportion choose McKinsey. But there is no point speculating on a forum like this, most of the differences pertain to style, industry focus and other issues that you can only really get into once you have an offer from the particular firms. If you are lucky enough to get the two offers, you will have plenty of time to sit down with the two firms and really get into the differences, which are often quite intangible. Until that point, anyone who comments on this forum will be trading in cliches and stereotypes that aren't really worth much to you.

I'm not speculating. In my country BCG interviewers usually ask "Why BCG?" and then (doesn't matter what you answer) "Why not McKinsey?".I just want to gather right facts for correct answer.

Curios,These debates usually don't lead anywhere useful. You further state "in my country...", this makes it even more pointless as different firms are perceived very differently in different countries. In the UK you'll be a very good candidate if you manage to sit both an interview with BCG and McK, exceptionally unique if you receive an offer from both. By that time you'll be smart enough and capable to make a choice. In reply to the interviewer's question on top of the differences that are pertinent to your country I wouldn't have any problems in stating that: "yes I have also applied to BCG as this is a very competitive job market and I have to expand my options". Honest and simple.

throw it back at them and show some confidence in your own choices - are they implying that BCG should be second choice?

It's a routine question and interviewer waits for routine answer (like: have you done your homework? yes, i have).They just don't like one another (BCG and McK).

Whichever partner asks that question has a big chip on their shoulder.If it were me I'd simply answer 'I've applied for both, they are both great firms and it'd be a privilege to work for either of them, I'm particularly keen on BCG for reasons x,y,z'If that isn't enough for them then they have a serious inferiority complex that would make me nervous about working for them. I would bet that more than 95% of people who apply to BCG also apply to McKinsey, and the interviewer is an idiot if they think otherwise.Of course, if you haven't applied for McKinsey then you should feel free to say why not and that can be the answer to your questions.