Kind of hard to address the original question without more info from OP. Which routes? How many miles do you expect to fly (enough to get 100k status)? Is money an object (presumably the case, otherwise you could just buy J?

In some cases it may make sense to go with an airline that offers frequent discounts on paid J, i.e. Continental to Europe, though that might not work depending on the routes. In other cases AA discount fares + Co-pay + miles might be cheaper. Or perhaps UA if you don't mind paying a higher base fare (though you will have trouble finding any upgrades to Australia in C using miles)

Yet another factor is the quality of the product. I would far prefer a lie-flat seat in NZ business class than the crappo UA and AA seats (though those will improve as they are replaced).