Knight and Hale's Basic Performance diaphragms are easy to blow and produce good volume. The straight-edged single, double and triple reed diaphragms are the easiest to learn and master. The fewer reeds a call features, the less air it takes to produce the desired results - therefore the easier it is to adapt to.
The Basic Performance series are perfect for the Beginner. Once mastered, moving up to level two or three calls is that much easier.