Importance of Variety for PhD Recommendation Letters I am a senior getting ready to apply to PhD programs in Applied Physics (I currently am located in and plan to attend grad school in the US). I am currently working a co-op at a large company in a small, very research-oriented and very academic group doing research that is directly applicable to what I want to study in grad school. The group lead and another researcher (both hold PhDs) have agreed to write letters of recommendation for me, and the third will be from a professor at my university. 

Today I was told that it could be more beneficial to have only one letter be from the place I work now (Company A), as having two letters from the same place (but different people) could be seen as redundant. I do have a former employer from "Company B" I could ask (who does have a PhD), and the main work at Company B is tangentially related to what I want to focus on in grad school, but I feel that while the letter will be strong and positive regardless of who it comes from out of these, it could be more beneficial to have a second letter come from Company A. I say this because I have been here longer (15 months vs. 6 months at the previous company) and have therefore taken a larger role, everyone I work with now publishes regularly unlike at Company B where the work was more focused on R&amp;D for product development, and both letter writers at Company A are well-connected in the field and more specifically this particular research topic. Additionally, I feel that the writers at Company A could comment more specifically on my research inclination, while at Company B it would be more focused on technical ability and hard work. Finally, I haven't been in touch with my employer from Company B, and while it would be straightforward to reestablish contact (and I'm sure they would respond positively), this could be considered a disadvantage.

My question is: Despite the fact that a second letter from the company I work for now could be slightly stronger compared to a letter from a previous employer, could having variety in my letters outweigh this?
Generally speaking, strength outweighs variety, with a caveat. If your two letters from Company A are both vary strong and they say different things about you, that's the way forward, especially if you think that the letter from Company B would be quite weak. However if both letters from Company A comment on your same attributes, discuss the same responsibilities and outcomes, and essentially tell the admissions committee the same thing twice, you are better off with the weaker but different company B letter.