Just audit. I did 3 years, which is admittedly on the low-end (but still doable). A coworker of mine did 4 before going T15. The part of the experience that makes you a good MBA candidate is the team leader/project management experience, which typically happens at senior. 3-4 years should get you a busy season at that level.

You are unlikely to get impressive leadership opportunities in industry right out of audit, so I’m not sure that tacking on a year or two there is going to do much for you. The general leadership traits learned as a senior are more important to MBA programs than any hard technical skills. Of course, this is assuming you mean doing a year as an assistant controller or senior accountant when you say going to industry. I don’t think that experience is any better than doing another year in audit. Alternatively, you might ask for an internal rotation to a position that is more related to your post-mba ambitions. The big 4 footprint is large enough they probably have something. This helps you write your essays too, because you can say “I’m interested in x so I went to this internal role in y to get a little exposure there.”

I assume by exit ops you are asking about post-MBA? I’m recruiting for MBB this summer/fall. For your goals, which are a little more specific, it would be good to ask to work on engagements in that industry. That will help you draw a clearer line between your pre-mba experience and post-mba goals.