You generally dash more often than you use your EX shot, so it may be more comfortable to have dash set to B (XB1)/Circle (PS4) and EX shoot to Y (XB1)/Triangle (PS4). One tip I do want to mention is that if you are having trouble with the controls using a controller, things may be easier if you swap the buttons for dash and EX shoot.
This guide's pretty cut and dry and covers the default buttons/keys for the keyboard, Xbox One, and PlayStation 4 controllers (for those using a PS4 controller on their PC).