Most US colleges require three letters of recommendation from prospective Masters students. There are two professors that I have worked with extensively in my institute, and I am sure that they can give me excellent recommendation letters based on my research work with them. The only other professors who can recommend me are professors with whom I have not interacted with too much outside class, and may not be able to give me much more than a "He performed excellently in my courses" recommendation. I do not feel that they can add much to what the first two professors say, seeing that I performed well in their courses too.
I worked at a large software company as an intern and left a very favourable impression with my manager there. He has said that he would be willing to write me strong letters detailing my teamwork, coding ability, communication skills and ability to work with tight timelines.
I wanted to know which letter MS programs in the US would value more as a third letter - the impersonal "He is a good student" from my professor or the more personal and authentic one from my internship manager.