My advice: you are in a position every candidate dreams of, so enjoy it and do not stress too much! You have a luxury of going into the BCG interview being calm and knowing you have ATK offer in your pocket (and I wouldn't call ATK tier 2, they are a top notch consulting company).
So, do the BCG interviews and you will see what happens. If they give you an offer, you will have time to think about it and decide. In case you will then think BCG would be a better fit for you, then you will just accept their offer, end of story. Consulting is a very competitve employer's market and everybody at ATK will understand. However, honestly I know people who decided for ATK against BCG, when they had both offers (because of different reasons, like industry focus of the particular office, culture, impressions from the interview, etc.), so just take your time and think about it when the moment arrives.
Thanks Daniel, logged into this website for the first time in a while. Thought it would be good to say thanks for the advice here! I ended up going with Kearney as it felt like a place where I would resonate well with the culture - after seeing your comment I was a lot more comfortable with my decision. Your advice could not have been more spot on. Since joining Kearney I have never looked back. A lot of the prep sites place so much focus on MBB vs. the rest for new grads, it almost feels like non-MBB offers shouldn't even be considered. And after a year and a half at Kearney, I would definitely encourage more prospective consultants to adopt a similar line of thinking. You can still get a top notch experience with (opinion) similar client exposure at a firm like Kearney.
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