What Keys, Everett? My Piano Ones! LOL For guitar, can also be any, for I like bar chords as well as the open ones.

When first starting to get a musical idea for a new song, it will be from playing certain chords or a riff, just going by tone color, not any key. Or, if I am starting to get a song come to me vocally, I will find the key I am singing or humming it in, and that's the key, unless I have to change the key later, if the high notes are out of my vocal range.

I have songs in most keys, though the song, (musically and/or vocally) dictating them.

My favorite key to play blues type songs though is C. Just because that;s the key I first started to play blues/jazz in at 12. So, I don't have to think about position or anything skill wise while playing that style.