Atlanta airport
New York City
O’Hare Airport
Orlando
Just Orlando for me.
All of them.
I’m British, if that makes a difference. I’ve been to all of them except O’Hare, but I will be there in May.
All but Orlando.
Over twenty visits to the USA over the past 25 years, and seen none of these…
Atlanta airport Yes
The Grand Canyon No
Los Angeles Yes
Las Vegas I was on a bus from Ft Irwin Ca to an airport outside of LV
New York City Of course
O’Hare Airport No
Orlando Yes
all except Orlando and LA.
Well, you did specify the airport in Atlanta, right?
From your list:
Atlanta (airport and city)
Grand Canyon
Los Angeles
Las Vegas
All except Atlanta were from a family vacation when I was a teenager, and yet I somehow think I’m reasonably well-traveled. I’ve been to Six Flags Over Texas, DisneyLand and Cedar Point. What more could a man want? 
I’ve been to:
Atlanta airport
New York City
O’Hare Airport
Orlando
I’ve been to Los Angeles, Orlando…and, uh, Merlin’s Shop of Mystical Wonders. For real.
O’Hare
LA Airport
I’ve been to FLorida, but not Orlando
Orlando and New York City
Note: For places where the city but not the airport is specified (LA, NYC), I’m giving a “yes” to “airport only” votes.
I am not giving “yeses” to “not yet but I will be next month” votes.
Atlanta airport: 28
Grand Canyon: 18
Los Angeles: 29
Las Vegas: 27
NYC: 37
O’Hare: 31
Orlando: 28
ETA: And for those who aren’t clear about it – O’Hare is in Chicago. It and Atlanta are the two biggest hub airports in the U.S.
Just Orlando.
All but Orlando. And I can’t imagine that will change any time soon.
All of 'em.
So far, just two:
NYC
Orlando
Which is depressing, because I consider myself quite well-travelled… I just haven’t seen much of the US, for some odd reason.
The same. I have never been to the Grand Canyon but have been to all the others multiple times.
I’ve been to all except Atlanta and O’Hare (although I have been to Chicago, just not via O’Hare). Admittedly, I was only 7 at the time we visited all of those places, but it still counts, right?