They should have:

* mixture of BIG and little knobs (big ones for mostly tweaked functions)

* enough space for your fingers

* be small enough for transportation

* logically layed out

* plenty of visual feedback (proper labels, could be printed/vinyl cut... lcd screen and plenty of leds showing button/switch status)

* sequence position feedback (for example a counter that counts bars and beats up to a specified number. You can change amount it counts up to)


could keep going but it would get expensive :)