Traveling from the US in September/October 2024. Planning on spending a week in Perth, then fly to Sydney or Melbourne and take 14 or 16 day tour. Would like some time in New Zealand also. Any suggestions appreciated.

Does your three weeks include NZ?

If you have 3 weeks only then stick with Australia. It's a BIG country and about the same size as the USA. However I think Perth is a bit dull for a whole week unless you were getting out of the city to the exciting places but then they are a long way from Perth which takes time and effort to get to.
New Zealand is awesome but it takes more effort to get here than you might think - there's 4000 km of Tasman Sea between us. Plan another trip for NZ!
You could have a lovely holiday on the east coast - Sydney and Melbourne both have their different charms and then head to Far North Queensland for the Great Barrier Reef and spectacular scenery. Brisbane is okay but more of a gateway to the Gold Coast and Sunshine Coasts. I live in Auckland and have been to Australia many times - my favourite part would be FN Queensland.
We did a GBR day trip from Port Douglas once to the outer reef and it was an incredible experience. We were swimming and snorkeling in the Coral Sea with no land in sight.

I agree. If you only have 3 weeks, stick with one country. As you're already going to Perth, that country would logically be Australia.Australia – size map: https://www.virtualoceania.net/austr...ustralia.shtml
Australia - Tourism: https://www.australia.com/en
You will need Visas. Use this link & apply now if you are coming this year: https://immi.homeaffairs.gov.au/visa...sa/visa-finder
You might also like to have a look at the Trip Advisor Australia Forum, which is a lot more active than this one.

Thanks so much for your comments. We’re stopping in Perth because our son and DIL live there, which is the main reason for our trip. Since we’re retired, we’re not limited to 3 weeks, just thought it might be a good time to consider as we begin planning. Thanks again.

From Sydney you could head north up the coast, or south. There are places to stay and small towns all along those areas. If you decided to drive, you could start in Melbourne and drive along the coast to Sydney, taking your time to explore the area. Beautiful beaches but too cold to swim.

Or from Melbourne, go inland to the old goldfield areas, there are heritage buildings in Ballarat and Bendigo. The Grampians is a good place to spot wildlife and do walks. Beechworth is another popular small town.

Do you particularly want to go on a tour? Or would you be happy to hire a car? One other thing is that if your dates coincide with school holidays, coastal accommodation will be harder to find. Each state has slightly different term dates.

Hi HNL,
Bang-on advice from all above - can't do better than locals.
Three weeks for one or the other country.

Australia: maybe mix oceanside locales with at least one Outback destination? Uluru is the obvious choice, well worth it.
Btw, in Perth plz say Hi for us to the Denham dolphins (i.e. Monkey Mia). Especially Jacky and Holly Fin, if they're still around.
The Great Ocean Road would be a must for me.
Never been to NZ, but we do watch endless drone and tripod footage of it nearly every week as we breakfast while watching Naturescapes TV channel.

I am done. the dingo

I agree, only visit Australia this time. 3 weeks is not enough time to visit Australia, let alone adding New Zealand to the mix! 3 weeks would be a struggle in New Zealand. Concentrate on a certain area of Australia and enjoy it to the max!