OP, do you hold some sort of instructor credential, or have any past EMS teaching experience? Many states require EMT course instructors to be credentialed, by taking a course on state standards and pedagogy, completing an internship with existing courses and often a set of examinations. With this experience you will be able to critically examine a text for it's merits and weaknesses and determine what best fits for your students and teaching style.
I highly recommend you seek out this training and experience, or at least work under an established instructor for some time before trying to figure things out yourself. If you'd like some help finding instructor resources, feel free to PM me.