What's according to you the best place to live with children and why?

Lot's of places spring to mind (I travelled the world extensively doing geophysical exploration work for decades)

Denmark, Esperance, Western Australia.

https://en.wikipedia.org/wiki/Denmark,_Western_Australia

https://en.wikipedia.org/wiki/Esperance,_Western_Australia

are small towns in a big (3x larger than Texas) Australian state.

Near zero COVID cases (by world standards) as the entire state went, Nope, screw that, and closed their borders (two roads and an airport) and kept on living life as per normal (with occasional bursts of masking up for the few cases that landed).

The south west of the state has good long term prospects re: climate, the area has forests, ocean, and hand tools.

Minimal pollution by world standards, relatively safe in many respects.

IT work from there is possible as is FiFo (fly in, fly out) work on massive global scale resource projects (iron, lithium, tin, LNG, etc).

It's a place where kids can ride bikes and work their way up to jumping off 50 foot sea cliffs into mammoth southern ocean waves - which is always fun:

https://www.youtube.com/watch?v=gViRfoNmGOg

https://www.youtube.com/watch?v=nFA6jUdJMb8

You can own a gun and shoot 5,000 yards ULR if you want (sans criminal record, domestic violence orders, etc), but there are very rarely mass shooting incidents | school shootings | car park arguments with guns, etc.

Close to their grandparents? (A friend of mine says their grandparents are always willing to be last-minute babysitters, or help out in case of an unforeseen emergency.)

I don't think it's as simple as the place with the best sunsets or the best air quality or any geographic features. Wherever you choose, the cost-of-living will determine a lot of what you can do. (Especially if you're saving for college, or even planning to travel with your family.) And of course, there's the quality of the schools, and who your kids will be hanging out with in their formative years as they're growing up.

If you're planning for the next 20 years, you might also want to take climate change into consideration. (If you end up in Arizona, you're almost certainly going to be spending much of your summers indoors....)

A place that isn’t polluted, dangerous, expensive. Children adapt, but that’s easier when they don’t face severe obstacles and hazards.

The data we have indicates the best environment for children is a stable two parent home with middle-class economic security. Parents who don’t abuse drugs or alcohol have better outcomes with children. Financial security probably proves harder to get and keep than finding the perfect geographic place.

For the USA, I would say a rural community within a hour's drive of a major airport/city. Near a town with common amenities and a public school with community expectations that all kids will go on to some form of higher education.

Of course, my version of best is just what I think is best for my kids and you are free to hold a differing opinion.

Where you think they should live as adults. That's the reason to stay in the rat race at a HCOL area. If the kids grow up local they'll have a built in network, and have the right attitude to make it as the next generation on the hamster wheel.