15's are my favorites. They have plenty of playing room and the buttons are usually big enough for your fingers. I am not a fan of the 21's . I find it better to own a couple harps rather than trying to make one size fit all. I also think they sound better.

AND I am a fan of the "L" wrenches rather than the "T"s. I think they are better for fine tuning because of the leverage they allow.

Are the buttons like golf Ts or white plastic trapezoids? Are the bars wooden or plastic and aluminum? Are the corners rounded or sharp?

Don