grad2032

I'm applying for a PhD in Computer Science. I have one letter of rec from a professor whose graduate student I did research with. I did not do any other research with any other professors. However, I do have 3 different bosses (from doing internships) from which I could get letters from. I plan to get one letter of rec from one of those bosses. But for the last letter of rec, I have a choice: either another boss who knows me well and my work ethic; or, from a professor. All my internships were doing software development. The first two were mainly just doing programming. The last one was developing a mobile application; but it could be related to research since no one in the company had prior experience in mobile app development, and I had the task of researching which platforms to use, etc. One of my professors remembers me and did say he would write a letter of rec. However, I'm afraid that he may not write a very strong letter, because I simply took his classes and did a group project with him (and my classmates). In addition, this professor is mainly a lecturer, not much of a researcher. Another professor said he would write a letter, but I only took 2 of his classes. Is it a no-brainer to simply get the last letter from a professor? Or should I seriously consider getting 2 letters from bosses since they probably know me better?