I am finalising my applications for Insead and Columbia Round 1 / ED.
Concerning recommendations I would like to use one from my current supervisor and the second one from my mentor (I got a full merit-based scholarship for my BSc studies from a FTSE 100 company. He is an MD at this company). While I am pretty sure about the first recommender, I am not so quite convinced about the second one. He knows me very well, but I have never worked with him. Do you think, that this would be still a good choice? Insead and Columbia ask namely for people who know you professionally.
Many thanks for your help
You should choose someone who knows you professionally and who you've worked with. You don't want to pick someone just because they have a good title; you need to pick someone who can write about how they've worked with you, what your strengths and weaknesses are, etc.
If this person is your mentor, I assume you've worked with him in some capacity. While it might not be the same professional capacity as a direct or indirect supervisor, he could still shed some light to AdComs about what you've been like to work with as a mentee, how you've faced difficult situations, etc. Can he say how you've worked with a team and how you've been to work with in a business situation? Maybe not.
Ultimately, there are trade-offs with any person you pick and you will have to consider your application as a whole to see if this person adds something to that. Keep in mind (as you know) deadlines are coming up in a few weeks. I assume you have already asked this person to write your letter; if not and you intend to ask him, you should ask him as soon as you can. If you intend to pick someone else (do you have anyone else in mind who you could ask?), then that person would at most have 2.5 to 3 weeks to write something. IMO, that's kind of short given people's work schedules, vacation plans, etc, but if you can do it, then go for it.