I agree with Henning's answer completely.
You must be 100% comfortable with the choice. Its your choice & career. Its good to get inputs and advice from various sources for sure.
I also always advice people to go for that option which is a better fit to your values, career aspirations and risk apetite. Choose that which will allow you to do your best and be joyful. Dont get into something for the wrong reasons- money, peer pressure, impatience. Focus on giving your best and let things happen.
As with every situation/event/choice in life, nothing will be perfect. Be mindful of this and work accordingly. Regardless of which job you take, there will be ups and downs and you cannot make that perfect choice as there will always be something a little better. So remove this pressure.
Overall, S& and ATK are both good places to work and will give decent exit opportunities. While they dont have the same level of pull as MBB, if you work a bit harder on your story and networking, landing a good exit option will be no problem. But before you get there, make sure you do well on the job, learn a lot, make a real diference at client & uplift life of people around you!