@d0loreshaze It’s up to you. I remember reading somewhere that Admissions Offices would prefer to see the letter that is more personalized and specific than a generic letter from a more well-known person. At the very selective colleges, Admissions Officers read through thousands upon thousands of applications per cycle, so a letter that isn’t more of the same (this applicant is great w/o specific evidence of how) would stand out compared to other applicants. Personally, I would ask your manager for a recommendation, b/c he is more likely to have specific examples of what you did and how you excelled at your internship.
Hope that helps! Good luck with admissions!