Complex Systems Prerequisites

What is the best training for work in complex systems, or the fields of complex systems?  If I could start over at the beginning of university, I would have studied physics and ecology––or some other messy, everything-effects-everything, field-based science.  The physics gives model-making, clean thinking, math chops (important), and lots of model systems.  The ecology gives experience with how messy life is, and how amazingly complicated natural phenomena are, all the simple, complex, horrible, beautiful ways that models can break, and much in the context of case studies.    

And a person who has encountered both appreciates that models are wrong and useful.  You actually get that from either field.  But appreciating that idea is not an all or nothing thing, and it can always be appreciated more.