12/2 MC cable.
But I suspect your job is being done in a different style, we daisy chain from fixture to fixture with MC cable.
I am guessing you are piping from fixture location to fixture location and dropping a single whip to each fixture.
If we were to do that we would order the fixtures equipped with whips from the factory.
I've seen a ton of specs that only allow MC no longer than 6'...which means the only use for MC would be for fixture whips.It is almost the only way it is done in this area, there is no code reason not to.