As a guitar teacher, I've been looking for the best approach to teach beginners how to play the guitar without their having to go through the frustrations that I encountered as a new player. I eventually found a method that starts students out in the key of G and uses some "flavor" chords to quickly enable the beginner to learn the I, IV, V and six minor chords in quick fashion. This gives them quick success on the instrument and also gives them confidence as they struggle through the more complicated chord-forms that are introduced later.
Hal Leonard produces several books for worship that fit nicely with this method. One I use often is "4 Chord Worship Songs for Guitar." The songs in this book are all in the key of G. This makes them easy to play using the basic chord shapes mentioned above. The caveat is that G is not always the best key for singing. We've gotten around this by using capos.