My favorite defaults are D and F, since they're the same on most (all?) keyboards, and they have the little ridge on the F so you have an easier time finding them (same as if you're typing).
One thing I usually do when I have non-customizable controls (e.g. because I'm in a hurry for a game jam), is to make it like fire1 is between two alternatives for fire2, so you can at least choose the left-to-right order without going to a menu. Example for an American keyboard: Z and C -> fire2, X -> fire1.
One thing I usually do when I have non-customizable controls (e.g. because I'm in a hurry for a game jam), is to make it like fire1 is between two alternatives for fire2, so you can at least choose the left-to-right order without going to a menu. Example for an American keyboard: Z and C -> fire2, X -> fire1.