Reference letter: boss or supervisor-esque coworker?

Is it better to get a reference letter from my actual boss, who I did not have as much interaction with, or my higher-up coworker that supervised me? My coworker definitely knows me much better as I worked closely with him and received all instructions, supervision, and training from him. I think my coworker would write me a better letter, but how bad would it look? Do mac and uoft care a lot about reference letters?