Importance of Variety for PhD Recommendation Letters
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.