Hi Sanjana28,
Congratulations on both acceptances! You're in a great position to be choosing between these two programs right now.
One factor that I would consider between ESSEC and INSEAD is global brand recognition. While ESSEC is a very well-respected school, the reality is that very few business people in the US have heard of it, whereas INSEAD has more widespread recognition. If you don't want to work in the US but do want to work elsewhere in the world outside of Europe, I would still say that INSEAD is more well-known, and that brand value counts for a lot with employers.
I'd be less concerned that the MIM program is newly established at INSEAD. While there may be a few kinks to work out with the program if you're in the inaugural class, the reality is that what really matters are the resources of the university, not just of this specific master's program. INSEAD in general has a very strong recruiting track record with top global consulting firms, so you would certainly benefit from that relationship even if you're in the MIM rather than the MBA program.
Ultimately, the choice boils down to what you personally are looking to gain from your master's experience. If you're considering a career switch (i.e. if you didn't do any consulting prior to your MIM) or if you want to explore certain academic or professional areas, a 2-year program would give you more latitude and time to accomplish that. If you're already laser-focused on what you want out of your master's degree and want to get to your goal as soon as possible, then a 1-year program will be a better fit for you because you'll spend less money and be out of the workforce for less time.
I hope that helps! Best of luck to you!
Best,
Doris