Not an expert, but I'd say the A.bidwillii is the hardiest....I've seen them growing beautifully in Western NSW where Winter temps of -10C (14F) are common.

Here is a link that might be useful: Bunya Bunya

Arauquoia,
from a tropical perspective, Araucaria bidwillii is certainly more inclined to tolerate colder temperatures than A. cunninghamii. The natural occurence of both species gives some clues to this phenomenon. Bunya Pine is an extremely rare species within tropical australia- it is actually only know from 2 locations with less than probably 200 mature trees, however Hoop Pine be it restricted in occurence to Fire refuges, is far more widespread within the tropical zone of Queenslands east coast. Bunya Pine is found only at reasonably high altitude in two locations west of Innisfail (south of Cairns and again north west of Cairns. Hoop Pine however occurs through Cape York and often grows near sea level in extensive sand dune systems and seasonal rainforests where fire is extremely infrequent or non existant.

Additionally, Bunya Pine is much more closely related to the Monkey Puzzle Pine from Chile which grows within the snow line. The stronghold of Bunya Pine is within SE QLD between the Sunshine Hinterland to the Bunya Mountains. It most certainly becomes cold during winter nights, certainly below 0 on the Bunya mountains.

The 2 locations of Bunya Pine within the Wet Tropics experience chill winter nights with the Mount Lewis population possibly reaching 5, especially as they occur within a gully system which would experience cold air draiange from the 1000m asl+ high mountain range above.

Adding to this both species probably would grow equally well in Tasmania, but YES bunya would be better suited.

Definetly go to the Botanic Gardens they have all sorts of Agathis and Araucaria- some massive Agathis macrophylla, as well as Mount Annan, which has a very good Wollemia growing now, much better than the Sydney specimen. Also go to Mt Tomah to the west of Sydney in the Blue Mountains- they apparently have Araucaria araucana.

There also is a massive (it really is) Araucaria columnaris within a park in the middle of Sydney- someone from Sydney may be able to help you here. I think its near Glebe ????.

Are you going elsewhere in Australia

Regards from Kris

Arauquoia, you might misinterpret Kris's description of the distribution of the Bunya pine. He is no doubt correct about its tropical distribution, but doesn't mention its subtropical distribution. I don't think the natural distribution of Bunyas would be as great as that of the Hoop Pine, but it's bigger than Kris's posting might have led you to believe, ranging from the Bunya mountains (North-west of Toowoomba)to the coast.
The range overlaps with that of the Hoop pine, the Bunyas preferring the higher ground. Both are plantation-grown (around Nanango and Blackbutt) for timber, but the Hoops are more common in forestry, being faster-growing.
A visit to the Bunya mountains would delight your heart. You could see Hoop and Bunya pines in their natural habitat. Bunyas have wonderful trunks, like giant elephants' legs. There are patches where they are the only tree, with an understory of ferns only. Would your trip "through Sydney" allow for a detour there? Toowoomba has street plantings of them both and of Norfolk Island Pines (I forget which Araucaria they are, but they grow as well here as Hoops and Bunyas) and a few splendid Agathis robusta as well, which you could see in passing.
What does hardy mean to you? Hardy to drought, cold, or both? At any rate, the Bunya would win out on both counts. Despite its natural habitat on well-drained basalt soil in rainforest (of a relatively low rainfall type), the Bunya grows well where it has been planted out on the poorly drained blacksoil plains where I think the frost gets to about -8 degrees. These plants were probably protected from frost when young. Neither are hardy to fire.
Don't forget to see some Wollemi Pines while you're in Sydney. Araucaria wollomensis or some such name. They're newly discovered, created quite a lot of fuss when it happened (the location is still secret) and only recently on the market. One of our local gardeners has amused and delighted all and sundry by entering his knee-high specimen in the "specimen tree" competition in the local spring Carnival! To his disgust, the judges couldn't find it when they came to his place.
Trish

They grow perfectly happily in Melbourne and Beechworth (which regularly gets snow).

Trish,
i did mention its subtropical description!

"The stronghold of Bunya Pine is within SE QLD between the Sunshine Hinterland to the Bunya Mountains. It most certainly becomes cold during winter nights, certainly below 0 on the Bunya mountains".

Araucaria wollomensis, I think you mean Wollemia nobilis, but the former sounds interesting enough !

Sorry, Wooroonooran! I'm gulty of careless reading - and of thinking that Wollemia was an Araucaria...... Didn't mean to peddle misinformation here! Is in the Araucariaceae family, or something else?
I suspect that little Bunya pines down in the forest don't have to cope with ) 0 degree temperatures. They'd be pretty sheltered down there in the forest floor microclimate of their natural habitat.
Trish