Who to ask to write letter of recommendation: the professor who knows me better or the one that gave me a better grade? I have a question in regard to choice of recommenders.

I'm applying to my dream school and I want to make the best choice for my LOR. I have two recommenders, one is a professor and he doesn't really know me, but I got an A in his class. Another one is a faculty, he knows me better than the other one, and he asked me a lot of questions in detail before writing the letter, but I only got a B in his class.

Which one should I choose to have him write me an LOR that's going to my dream school?

PS. I asked them both because I wasn't sure which one would be willing to write me the letter, but I only need one letter.
The B instructor's letter is promising; it may be more insightful and more diligent. An impersonal letter that says "the student earned an A" may not sway any admissions committee. You could even inquire directly whether or not he's going to mention the B grade in the letter.