Joint degree is a waste of time, money and effort unless you are very passionate about the course content. If you can get to a top business school, it will open the required doors. That's the reason you will see top business school grads at most of the top jobs. Good luck!
I agree with the poster above (aside from the shameless plug) that a dual-degree is a waste. You need to research the faculty that each program has and find someone you would want to study under. The "top school" thing is pretty useless as most of your cohort will be in the same position as you. The ideal place would be one that has a faculty with congruent interests to yours, a well respected research reputation, and most importantly connections. While I do understand the draw for large companies that a massive cohort offers, I cannot, at the same time, imagine being in a graduating class of 400 people. BTW I am interested in global macro.
Best of luck with your decision.