But then there's also 2B and 2H. A 2B would be awesome since it's so soft, a 2H on the other hand... you'd have a hard time seeing your own marks on the test, let alone the scantron machine.
I work as a teacher at a high school that uses a lot of multiple guess testing, and it's amazing what you a good scantron will pick up... good erasure is very important however, as if there are two sensed answers for one question, it marks that one wrong - unless AAMC uses computerized scanning where it can discriminate somewhat better.