[Solo Kazuki]

Game have also keyboard selection of weapons on F1-F10 keys if fast selection is required.
It's hard to chose "most used" weapons because there are three types of missiles, three types of bombs, two types of mines, flares and mega bomb. So both personal preferences and what You get as bonus make this selection very hard.

Edit: Most logic shortcuts selection is by types wrapped around. It requires only 5 combinations, e.g. REV+x, REV+y, FF+x,FF+y and REV+FF.

So something like (it's just example):
RED = gun
BLUE = 2nd weapon
GREEN = normal selection like [RSHIFT]
FF+GREEN = missiles A-C like [F1]-[F2]-[F3]-[F1]...
FF+YELLOW = bombs 1-3 like [F4]-[F5]-[F6]-[F4]...
REV+GREEN = mines 1-2 like [F7]-[F8]-[F7]...
REV+YELLOW = flares as [F9]
FF+REV = mega bomb as [F10]
would be nice

or if it's not possible
...
FF+GREEN = [F1] (and you select exact type by pressing GREEN)
FF+YELLOW = [F4]
REV+GREEN = [F7]
REV+YELLOW = [F9]
FF+REV = [F10]

Edit+: Just some random thoughts.
Sometimes You need fast select flares, so maybe YELLOW as [F9] and then REV+YELLOW should be [F10].