For me, Los Angeles.
New York is an awesome city, much safer than it was 20 years ago. Basically the opposite of Detroit…
If you do go, remember not to pee on the Alamo, they get touchy about it and may put you in jail.
I would visit the Alamo in the summer, so if I order apple pie in San Antonio I would include ice cream: remember the Ala mode. 
Never been to L.A and you call yourself an American!? That is like never driving or ever had sex and calling yourself an adult. The audacity! I’m just jesting, I had never been to New York City until fairly recently. Imagine that! Now it would Houston. In no hurry.
Sorry but how does this make sense?
NYC is a 30 minute bus ride away. I’ve been there hundreds of times.
Houston
So you answer is actually NYC.
Same here. Had I opted for San Diego instead of Great Lakes for basic training, I’d likely answer Phoenix instead.
I’ve been undressed by kings and I’ve seen some things. That a woman ain’t s’posed to see. I’ve been to paradise, but I’ve never been to me.
LA. I’ve never been west of the Mississippi. Or Manchester, if I’m talking about the country of my birth.
Leeds, West Yorkshire. Population 750,000.
The top four being London, Birmingham, Manchester, Liverpool - even though two of those four I have only ever visited for football matches and not stayed the night in.
This uses Primary Urban Areas as the definition of City as per use by HM Government for statistical and macro-planning purposes.
I’ve been to 4 out of the top 5 in the US, but never made it to Houston. No reason to, really. I’ve never heard anyone say “You really ought to visit Houston some time!”
Houston is so Anytown, USA it’s almost scary. Other than the belt buckles you could be anyplace in the country (except, say, Honolulu).
I’ve never been to LA, number 2 on the list, but I haven’t spent much time on the west coast.
Going by the ‘airports don’t count’ measure, my answer is Chicago.
If you throw that out, it would be San Antonio, as I’ve been to the airports in Chicago and Houston, and ridden a train through Philadelphia (and actually set foot in Phoenix).
Of the US top ten, I’ve been to 1, 3, 5 and 8.
The largest city I’ve actually lived in is number 81, Norfolk VA (though I spend a couple months in San Diego, number 8).
To finish the list of the ten largest US cities I have visited I have to go down to number 30.
#54 in the US–Honolulu. Also the only state I’ve never visited.
Charlotte, North Carolina (792,862)
Chicago