I'd say the most used are:
WASD + mouse (if you need more buttons, Q, E, ctrl, shift and space)
Or
Arrows + Z, X, C and space
I usually add both controls as they don't overlap. As jam game is often played in browser, player usually has mouse in hand so WASD may have the least friction.
Also do use same same input method in menu as ingame.
Edit: The worst key bindings in game I've seen were WASDQE without mouse. My left hand cramped while right hand had nothing to do :D