Letter of recommendation for grad. school application source

I am applying for admission to the Master's program next fall. However I am in doubt about the source of reference. I have two options: 1) My mentor at a research institute who was pursuing his Phd. when I was an research intern. However, he did not complete his Phd. 2) Research Scientist(Phd.) at my current organization where my role is that of a software developer. Therefore the recommendation is based on my work as a developer rather than on my research contributions. Both are willing to write strong recommendations for me. Who would be a better source of recommendation?