If you want to maximise your frequent flyer earnings from car rentals, it's worth checking how points are accrued with different companies.
Car Hire companies calculate points earnings very differently from how airlines do it.
If you're a member of several different airline programs, it's also worth checking which program earns the most points with different car hire companies.
The length and cost of your car rental will determine which program is best. That's because some programs get points per dollar, some per day, and some per rental.
So a short, cheap rental at the weekend should go to an airline where you earn points per rental, while an extended or expensive rental would get you more points by funnelling it to a per-dollar or per-day partner.
For example, a thirty-day car rental with Avis in New Zealand would earn you just 700 Qantas Frequent Flyer points, while you'd get a whopping 75 Air New Zealand Airpoints dollars (equivalent to thousands of Qantas Frequent Flyer points) if you put the rental to that program.
(To compare between programs as different as Qantas' and Air NZ's, we compared Hilton's HHonors point exchanges for the two airlines. 10,000 Hilton HHonors points will get you 20 Airpoints dollars or 1,500 Qantas points. Put another way, an Economy to Premium Economy upgrade from NZ to the USA is 250 Airpoints dollars.)
That's a huge difference in relative value you'll get by picking the most lucrative frequent flyer account to bank the miles. (There'll be a reduction in the exact amount between Australian and NZ Airpoints dollars, but the point itself is still valid.)
Of course, if you're renting a car inside Australia, things might be different. You earn 3 Qantas points per dollar spent or 2.5 Airpoints Dollars a day. So, if you're renting something expensive, you might prefer to funnel your rental towards Qantas, whereas if you've got a cheap deal, Airpoints might be the better deal.
Your individual situation will doubtless depend on your own frequent flyer program portfolio, so check what you'd earn for your accounts with (say) Qantas Frequent Flyer, Virgin Australia Velocity, Singapore Airlines KrisFlyer, Air New Zealand Airpoints, Emirates Skywards or Thai Royal Orchid Plus.
Here are some examples of what you'll earn from the two biggest car rental companies in selected airlines' frequent flyer programs.
Notably, Avis' airline partners don't include Virgin Australia.
Qantas Frequent Flyers get 3 points per dollar in Australia, or 700 points per rental overseas.
Air New Zealand Airpoints members get 2.5 dollars per day's rental worldwide.
Emirates Skywards members receive 500 miles on all rentals, and also get discounts when booking through Avis directly.
Avis also has many "other" partners for Australians, so don't forget to check whether you'd rather have American Express, Westpac, Citibank or Diners Club points -- but check the terms and conditions carefully.
Notably, Hertz's airline partners don't include Qantas.
Within Australia and NZ, Hertz gives you Velocity points per dollar for your car hire. (5 points for Gold members, 4 for Silvers, and 3 for Red members.) Internationally, you get 800 Velocity points per hire.
Air New Zealand's Airpoints members, however, get 2.5 Airpoints Dollars per rental day -- though not for prepaid rentals.
Emirates' Skywards frequent flyers get 500 miles per Hertz rental (or 1000 for the snazzy Prestige Collection). Skywards members also get discounts when booking through Hertz and free membership to Hertz's #1 Club Gold, which means that (at Gold locations) you just walk up to your prepared car and drive away without faffing with paperwork.
Cathay Pacific's frequent flyers get 500 miles per rental outside Asia, or 250 miles inside Asia.