In my many years of doing campfire singalongs and RenFest busking, I've come to refer to G as "The People's Key of G." It's a good range for *most* folks, the three-chords-and-a-cloud-of-dust I-IV-V combo of G, C, D (with Em for the bridge) is easy to play for long periods of time without cramping. Beginning players can jam along pretty easily, too, since the chords are different enough looking from each other that you can tell the difference by firelight.