Former Employer or Prof from Another Department?

[JonoJonnyJon]

So, I'm currently in the process of applying to an MS in Computer Science (non-research), but my undergraduate degree was liberal arts-related. Last year, I took some pre-requisite courses at a local community college. Since this past summer, I've started a post-bac program in Computer Science at a local state university. 

That's where my dilemma lies. I haven't really had enough time to form proper relationships with any of my CS professors. I speak up in class and have, so far, made straight A's in all of my courses, but none of them know me on a personal level.  Luckily, one of my tenured maths professors has agreed to write me a letter - I know that it'll be a strong one. I think I'll be able to ask another one of my former professors from the program to write the second one.

As for the third, I'm not sure who to ask. I can try my former boss, but I'm not sure if this will hold much clout. The company I worked for was a mid-sized tech company who, at this point, is very well known. My position wasn't completely tech-oriented, but there were certainly tech/quantitative elements involved (i.e. QA and product testing stuff). Another option is asking a professor from my undergraduate university. I took 4 courses with him, and he was my supervisor when I studied abroad. He knows me very well, and he's also held in extremely high regard in his field... which is Russian Studies, a field that has absolutely nothing in common with CS. 

Which do you think would be a better option? I would appreciate any help, I'm really lost on this one. Thanks in advance!