I love NZ very much. Wonderful people and amazing natural geography. But Australia has higher incomes and more career opportunities and would still be considered a huge career downgrade for many US citizens which probably still favors relocation to the more liberal US cities/states. The city/inner burbs of the major Aus cities are going to be reasonably liberal (in the American sense) and very multicultural probably more so than most of New Zealand outside Aukland. Aus has ridiculously high immigration rates but can be difficult to qualify. NZ currently has a conservative government keeping the divisive culture wars alive while Australia has a centrist Labor federal government as do the majority of Australian states.