Biggest actually works here - here is the usage of "biggest". See number 1.
adjective, bigger, biggest.
1.
large, as in size, height, width, or amount:
a big house; a big quantity.
2.
of major concern, importance, gravity, or the like:
a big problem.
3.
outstanding for a specified quality:
a big liar; a big success.
4.
important, as in influence, standing, or wealth:
a big man in his field.
5.
grown-up; mature:
big enough to know better.
6.
elder:
my big sister.
7.
doing business or conducted on a large scale; major in size or importance:
big government.