all depends on what you want , orange breasts are the same size , cordons , double bars, cubans all the small ones shopuld be fine. red face parrot finches even...pete
for the record, none of the foreign finch species available in Australia need licenses. Only natives, and only certain natives in certain areas/states.
Re the killer instinct birds of yesteryear. Perhaps the reason they seem to exist less is simply that we keep and breed those with nice natures, and sell off those who are nasty to people who just want colour. (While warning them of course.)
LML