For law school, GPA and LSAT score are very important. Business is probably easier to get a high GPA with, but engineering majors tend to score higher on the LSAT.
I don't think that's because of a systemic difference in how well the programs prepare you though. The fact is that it takes a lot more studying skill to graduate with an engineering major, so all of those who don't manage will be weeded out before taking the LSAT. They won't take it as an engineering student.
Therefore, on average, engineers will score higher because those that remain will be that much better at studying. But an equally talented business student will probably do just as well.