We have a visiting faculty in our department, her main research area encompassing Embedded Systems, which happens to be my area of research as well. I have worked with her on my Minor Project (Undergraduate). I asked her if she could write a recommendation letter for me, and she said she sure can but I should approach other Professors/Assistant Professors who are not a guest faculty in my department. (She doesn't yet have that "Prof." in front of her name.)
There is one more Professor, with whom I haven't worked but have taken four-five courses and hence he knows a lot about me and my abilities. However, since I am applying for MS, prior research experience of course matters. Also, the problem is that that Professor's field doesn't include Embedded Systems.
And since my research field is going to be related to Embedded Systems, wouldn't it be better to get it from the teacher who teaches Embedded Systems and with whom I have worked?
I am confused as to which faculty to get the reference letter from. Would it be beneficial to get it from the teacher I have worked with but is a visiting teacher?