We are planning a family vacation to North Queensland in July. We have never been to Australia, with teenagers should we go to Brisbane ? Cairns ? other ?

I have never been to Brisbane and I have not been to Cairns/Port Douglas since 1991. However, I too am taking teens to Australia this summer (August) and the answer was easy for me -- Port Douglas (an hour north of Cairns). Brisbane does not give you access to the Great Barrier Reef or the Daintree Rainforest. It will also be cooler in Brisbane in July, not really ideal beach weather. As for the theme parks nearer to Brisbane, my own approach is hat I am not flying 1/2 way around the world to make a special trip to a theme park. In our case, we are from NY and we can fly to Disney World and Universal Studios in 2 1/2 hours. Bottomline -- based on my research no contest. Port Douglas/Cairns without hesitation. Perhaps someone who has spent time in both places recently will offer a different perspective.

One moe thing -- Brisbane is not North Queensland.

As mentioned above, Cairns/Port Douglas weather in July is far balmier(avg daily temperature 61F-78F) than that of Brisbane in SE Queensland, some 1700kms south. With the combination of summer vacation times in USA and Europe, and Australians from southern states escaping their chilly winters, it's the busiest time of year in Far North Queensland. So do book your accommodation well in advance.

go to cairns.

I went to Surfer's Paradise (just south of Brisbane), and Cairns with my kids last August. Add another vote to Cairns and surrounding area. The weather will be warmer, and we enjoyed the activities more in FNQ.

Thanks to all...we are off to Cairns, does not sound like we will miss much if we pass on Brisbane this cycle( and we were able to insert a few days in Sydney as well)

They are so totaly different, brisbane is a large city, you can head north easily to the Sunshine Coast, Noosa and places, for lots of things for families the Gold Coast, I really like cairns and nice to drive around the beaches like Yorkies and up further to Port Douglas, but it really depends so much on how you want to spend your time and whether you want a large city with time spend at busy beach areas or you want a smaller place like Cairns.
Time for the 'family vote' ( serious! - we do it ), make sure everyone can add in how they want to spend the time so everyone is happy.
I guess it depends also where you are coming from ? You might well find yourself flying in to Brisbane anyway so you could easily do both.

I have been to both places and my vote goes to Cairns. The Great Barrier Reef, Daintree Rainforest and beautiful tropical beaches beat amusment parks and Surfers Paradise hands down.