Your choices for a citation style?
The Bluebook. The Greenbook. The Maroonbook. Plus others, which you'll find listed in an article at the University of North Texas: "Citing Legal Materials/Legal Style Manuals."
What's important isn't so much the one you use, but that you choose one and use it consistently throughout any single document.
Otherwise, you'll look sloppy, an impression that will cast your legal reasoning in a negative light.
Further reading: "Communicating Your Authority," by Maureen B. Collins, Illinois Bar Journal, 12/03.