Most law schools are reluctant to hire candidates straight out of law school, unless the candidate has a Ph.D. in an allied field. Even then, most would prefer that the candidate get some 'seasoning' before making the transition from student to teacher, but are relatively indifferent to what form it takes. What makes the most sense depends on your own situation and interests. The three most common paths these days are a one- or two-year clerkship, two or three years as a practicing lawyer, and a post-J.D. fellowship at a law school.