<p>Consider sending both letters. USC clearly states that they will accept a second letter. I am aware of one other selective college that “requires” one but will accept a second, and even a third letter. When asked about additional letters, colleges are likely to say something to the effect that a second letter won’t give you an advantage over a student who has sent one. They will also say that if the letters serve to clarify different sides of your academic persona then they would be helpful. If in doubt about whether or not a second letter is welcome, send a brief note to admissions and ask.</p>