In pop guitar styles (blues, folk, rock, etc.) keys centering on the four lowest open strings are probably the favorites, e.g., E major and minor, A major and minor, and D and G major; reason being that you don't have to play barre chords.

Open tunings change it up a little as several such omit the third, so can sound either major or minor depending on context, and can be played with simple barres formed by a finger or slide. Capos, of course, make it possible to easily play in any key.

Jeff Beck messes up the curve a bit by tuning his guitar to Eb, but who cares what he thinks? cool

R.

"My primary musical instrument is the personal computer."