Who should I ask to write a letter or recommendation I am applying for tenure track faculty jobs and postdocs.  I am setting up my letters of recommendation and I am struggling on who I should ask. I have one strong letter from my advisor, one decent letter from a professor but I am stuck on who I should ask for the third letter.  I think I have three options

Person A is someone I worked with recently and the work I did for them funded my PhD.  They are not a professor and do not have a PhD. This job involved a lot of practical work and could have led to some publications in journals (think higher ed research, while my phd is in statistics).  But it ultimately did not - we did have some conference presentations.  

Person B is my Master's advisor from four years ago. They are a tenured professor- and could speak well of my work from four years ago. 

Person C is another professor from my department but I don't think their letter will say a whole lot.  

From the link below it seems like person B would be a better choice as they are tenured and familiar with research I have done. I have asked person A for a letter, and they unexpectedly sent it to me. While it was very complimentary - it seemed better suited for an industry job rather than an academic job. 

Who should write a recommendation letter?
The two key criteria here are


Familiarity with your work (research, teaching, service). You want them to provide details for how promising your research is, how you would work with colleagues, how you'd teach and mentor students, and so on. 
Familiarity with academic work (tenure-track or tenured professors > other kinds of recommendations). From the perspective of credibility, someone who is familiar with the positions you apply for will be more readily believed when they recommend you. Also, they'll be more likely to mention details that speak directly to the position you'll serve in. 


Based on these items, person B would be best suited to provide a recommendation for you. They are familiar with your work from some time ago, and hopefully you've kept in contact enough that they'd like to provide a recommendation. (Writing them a precis or summary of your recent work will undoubtedly help, as they could also write at least a little about how you've performed since your Master.) 

Person A's helpfulness would really depend on the position you apply to. A's letter is riskier because some hiring committees may question the applicability of the letter on the grounds you mention - it may make it look like you're more interested in industry work. Person C is right out - a generic recommendation letter does you fewer favors, as the impression might be, "Wow, that person really didn't like the applicant." 

For other readers or for future planning: if you haven't had anyone observe your teaching, try inviting a letter writer to do that. Teaching may or may not be a central focus of the positions you apply to, but having someone able to speak more about your teaching may provide you with that third recommender if you only have two faculty members who have close knowledge of your research.