I'm notating a simple rock song that's in the key of A (monophonic bass line only.) The chords are mostly A, G and C and the melody has many C and G naturals in it. If I use the key signature of A, which most accurately indicates the true tonal center I have to use a lot of accidentals all the way through to cancel out the sharps. If I if I use no key signature I'll only need to use a couple of accidentals, which will make it more readable by the person I'm doing this for, who is not a strong reader or player. On the other hand, this makes it look like it's in the key of C, which is not the case. Similarly, I could use the KS of D major which fits in with the somewhat Mixolydian flavored chord progression, but doesn't reflect the tonal center. I run up against this in many bluesy or modal things, where the "proper" key signature may be messier than using a "wrong" one. What's the best or most common practice? Is it about accuracy of presentation or readability?