From my limited experience having gone through applications, I think that no doubt, IB and MC (Management Consulting) are the main "feeders" into an MBA. On the one hand, MBA programs love having people from these industries. On the other, well, there are lots of applicants from those industries so setting yourself apart becomes an issue.
If you go to government, you'll be going the non-traditional route. It's a gamble--you'll certainly set yourself apart from many other applicants, but that doesn't mean it's better or worse. I'm non-traditional (entrepreneur) and it worked out for me. You should probably talk to the admissions consultants in the "admissions consultants" forum and ask what they think.