(This is for grad school applications) I'll have one strong letter of recommendation from a previous research advisor, so I'm wondering about my choice of second letter. One option is a prof who works closely with my previous advisor. He knows me reasonably well and could write a good letter, but his experience with me is the same as the first prof and it would probably be mostly a rehash of the first letter. The other alternative is to use a prof I've taken a few classes with. He doesn't know me as well, but he's been impressed by my assignments/tests in his classes. He works in a different field from the first two profs, so it would give a little more diversity. I guess it might not make a huge difference in the end, but which one is likely better? A "redundant" letter from someone who knows me well, or a "diverse" letter from someone who doesn't know me as well?