Great question! Here are my thoughts...very much aligned with Jeanne's comments.
(full disclosure - I don't have an MBA myself and have no plans to pursue one)
In my opinion, you'd be better served to get several years of work experience before pursuing an MBA, for two key reasons:
1) Having work experience, particularly at a prestigious firm (you mention Wall Street), will help you stand out in the very crowded pool of applicants to top-tier business schools...this is of course in addition to strong scores on your GMAT exam, etc.
2) Having work experience will also make your MBA experience, wherever it may be, much more valuable and applicable. As I understand it, the real value of an MBA is the dialogue that takes place in the classroom, where your peers share their diverse insights on business topics based on what they've seen and lived in the real-world. You'd no doubt learn a lot from business school coming straight from undergrad, but it would again be more of an academic exercise, just learning the theory. If you come in with real world experience, the objective becomes much more practical, learning how to apply the theory you are learning to actual scenarios.
Hope that helps...good luck to you in whatever you decide to do!