If you want to do M/B/B consulting after law school, it will be hard to do unless you go to HYSCCN. Going to UCLA Law will make it very difficult for both MBB consulting and big law both(before the biglaw bubble burst, about 40% of UCLA got into biglaw; it will probably be 20% or less in the future). Also, it is very difficult/borderline impossible to get into a top-15 business school straight out of undergrad. Less than 1% of students going to these programs are straight out of undergrad. They specifically want people with several years of business experience. Whereas the LSAT will get you a spot at HYSCCN, the GMAT only serves to disqualify you.
A typical top-MBA class is 1/3 finance people, 1/3 consulting, and then 1/3 other. The 1/3 other are either military, Peace Corps, or from professional jobs such as not-for-profit office jobs or Fortune 500 non-banking/consulting jobs (such as financial analyst for PepsiCo, or General Electric rotational finance; for the purpose of this post, consider "finance" to be investment banking, private equity, hedge funds, and venture capital). Not-for-profit might be the easiest way to get in, because you'll be competing against other applicants from not-for-profit. If you're a banker, you'll be competing against bankers for the third of the class that is reserved for bankers, and a large percentage of them will have no problem getting 700+ GMAT scores and good letters of rec. And most of the people going to a top-tier MBA program that aren't already from finance or consulting are doing it to get into finance/consulting.
MBA programs are hardly used for anything other than to get a promotion in finance and consulting, and you won't learn very much other than things finance people and consultants want to know. In fact, one of the most popular classes at Harvard Business School is a class where you learn how to do case studies for a private equity associate interview.
People go to law school to get smart.