After learning the Majors in front row, 7ths in second, and minors in the third, which is more like the chord buttons on an accordian, I find that I am much faster than those with the majors in the second and if I can't get to the relative seventh with my thumb, I have its whole note under my middle finger. You will need to understand the circle of fifths and then make your own decision. The current 21 chord Autoharps allow you to move both the bars and the chord buttons to any position,although you can expose more of the bar by simply placing a short section of leather shoe lace under each button, and use a fine point marker to label the buttons on the side of the button facing up. That way they don't wear off, unlike buttons labeled on the top.

Also many people manufacture or order a Bm, F#m, and an E chord bars in place of the Ab, Eb, and Bb7 to give them more popular keys.

I would check with the Autoharp Page which has taken over for the original Cyberpluckers page and has tons of information for you to read, and modify according to you wishes. Although they are many ways to set up your chord bars, in my experience there are two most often used, Majors in the Middle, which does give you a home key and Majors Foreward which gives you speed.