umm... make them as personal as you can, but send them out to everyone. I had a few friends get big law jobs (non-t14, but t25) and that was the approach they took. I didnt end up with one, but i got an offer to skip oci the next year and come right in for a callback interview. It translated into a great job offer for my 2L summer, so whatever. Just put in as much time as you can, but obviously grades are more important then firms at this point, so dont put off your studies making your cover letters.