Best undergraduate majors for an aspiring lawyer/legislator?

A lot of law schools look for someone who takes a challenging curriculum. Political science has its benefits, but it also has a poor reputation when it comes to how challenging the course load is. You'd probably be better off taking a hard science, engineering, or something else that proves you're capable of doing hard work. You can minor in political science or something similar to show you have that interest though.

Because of your goals, I would suggest studying Political Science, Public Policy, Public Affairs, Government, or a related field.  I majored in Political Science in undergrad and the courses you will take (for instance Constitutional Law) will help you in law school as well as when you're a legislator.  Also keep in mind that there are internships that are only available to students with certain majors, so while you can major in a hard science or some other field, the government-type internships that will help you with the connections you need will not typically be available to you.  You will find some that only require a major OR minor in one of the above-referenced fields, but a major definitely helps.