An ASM Lead instructor has EMT or higher in medical knowledge. A certified instructor who has been teaching for a while and getting good reviews can also become a Lead instructor. The only thing a Lead instructor can do that a Certified instructor can not do is teach alone.

If you are looking for someone to put a class together for you you can choose any level of instructor to do that but keep in mind that if the instructor you are working with is not a Lead or Instructor Trainer, one will need to be found to help teach the class.