[lowercased]

True. Was thinking more about the G - again, another common pianoish base (in my experience, anyway).

D/E/A - again, ime - were always "guitarish" songs. GCF always seemed to be more "pianoish". Just my own observation/experience - it may not be true of everything, but seems to be true about much of the stuff I've listened to (and tried to play).

[elektronaut]

Yeah, C major (C/F/G) can be a bit awkward on guitar, the F barre chord is a painful hurdle for new players to get over.

A major (A/D/E) is probably the easiest key to play. G major is arguably the most useful, because you have access to all the important chords in open position: G, Am, C, D, Em.