I suspect it isn't easy to answer this question as you would need to consider a number of things:
(i) Perception by the general public that in a crisis the larger banks are more safer.
(ii) The govt will doing anything to save the 4 pillars, and probably doesn't a stuff about smaller banks.
(iii) The credit unions rely less upon wholesale funding as compared to the big banks.
(iv) The bigger banks are more exposed to derivatives.
(v) As in 2008, the govt will probably guarantee wholesale funding for all banks, but charge the smaller banks more.
(vi) The history of failure of smaller credit unions, building societies etc around Australia.
(vii) Some credit unions are better managed than others.
(viii) A housing crisis would affect the big 4 more, I think, as they own 80% of all housing loans.
At the end of the day the govt protection may make the big banks the safer option, although the govt itself isn't travelling too well at the moment .
Timber1956 (exbank employee) who frequents the gold thread may have a better understanding of the risk than I do...you may want to pose your question there.
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