Who should I have write my 3rd LOR, professor or former boss?

[Ew1234]

Hi! I'm applying for MA programs in comm/media studies, and am applying to a couple of programs that require three LOR. I already have two confirmed, and am hoping to get some advice on who I should ask to provide my third LOR.

I studied Advertising in undergrad, and two of my professors from the department have agreed to write a LOR. Both of them know me well. For my third LOR, i'm torn between asking another former professor who also knows me well but does not have a PhD (he is a lecturer in the creative track of our program), or my former boss. This person was my boss at an advertising agency, but she also has a PhD in psychology. We have a close relationship, and I'm leaning towards asking her.

Any advice is very much appreciated! Thanks so much!