I have completed both the UNSW Masters and a MBA... Unless you are specifically looking for aviation safety related subjects my advice is that a MBA gives you a broader knowledge base over the aviation specific subjects. With relevant aviation experience completing an MBA will give you the ability to apply an aviation slant on things anyway.
Usually these degrees start with a Graduate Certificate (4 subjects), Diploma (4 additional subjects) and finally masters (4 more subjects). The Grad certificate is a good way to get back into the swing of things or try studying for the first time and usually involve less intense subjects like Marketing, Leadership and alike before getting into the financial stuff in the diploma.
I enjoyed both degrees but felt in some subjects in the aviation masters it was like being told to suck eggs when it came to things like Airport (Carpark) Design and CRM. Easily the best subject in the Masters of Aviation at UNSW is Ron Bastch's aviation law which gives and excellent insight and understanding around the legal framework (Contract, Torts, Criminal) in which airlines operate.
Assignments in the Aviations Masters are relatively easy and are not graded the same way as an undergraduate degree with less focus on structure. Assignments in the MBA are more collaborative in group work so you won't feel like you are on your own.
If you have any questions feel free to send me a message. I also realise the irony of my spelling and grammar with the aforementioned degrees, but I can't be bothered proof reading...